Diagnosis system for vane-type variable valve timing controller

ABSTRACT

One-way valves are provided in a hydraulic pressure supply passage in an advance hydraulic chamber and a hydraulic pressure supply passage in a retard hydraulic chamber respectively. A drain oil passage bypassing each of the one-way valves is provided in the hydraulic pressure supply passage in the each hydraulic chamber to be in parallel therewith. A drain switching valve is provided in the each drain oil passage. A drain switching control function for switching the hydraulic pressure driving the each drain switching valve is integral with a function of the hydraulic control valve for controlling the hydraulic pressure supplied to the advance hydraulic chamber and the retard hydraulic chamber. It is determined whether the responsiveness of an advance/retard operation is in a normal range based upon a changing rate of the VTC displacement angle during advance/retard operating, thereby determining presence/absence of abnormality in the advance/retard operation.

CROSS REFERENCE TO RELATED APPLICATION

This application is based on Japanese Patent Applications No. 2006-119354 filed on Apr. 24, 2006, No. 2006-122763 filed on Apr. 27, 2006, and No. 2006-124825 filed on Apr. 28, 2006, the disclosures of which are incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to a diagnosis system for a vane-type variable valve timing controller in which one-way valves are disposed in a hydraulic supply passage of an advance hydraulic chamber and in a hydraulic supply passage of a retard hydraulic chamber respectively for preventing reverse flow of operating oil from the respective hydraulic chambers.

BACKGROUND OF THE INVENTION

A basic arrangement of a vane-type variable valve timing controller is, as shown in U.S. Pat. No. 6,330,870B1, adapted in such a manner that a housing rotating in a timed relation to a crank shaft of an engine is disposed coaxially with a vane rotor connected to a cam shaft of an intake valve (or exhaust valve) and a plurality of vane-accommodating chambers formed in the housing respectively are divided into an advance hydraulic chamber and a retard hydraulic chamber by vanes (blade portions) at the outer periphery of the vane rotor. In addition, the hydraulic pressure in each hydraulic chamber is designed to be controlled by a hydraulic control valve to rotate the vane rotor relative to the housing, so that a displacement angle of the cam shaft (cam shaft phase) to the crankshaft is varied to variably control valve timing.

In such vane-type variable valve timing controller, at the time of opening/closing the intake valve or the exhaust valve during engine operating, fluctuations of friction torque which the cam shaft receives from the intake valve or the exhaust valve are transmitted to the vane rotor. In consequence, torque fluctuations in the retard direction or in the advance direction are exerted on the vane rotor. Thereby, when the vane rotor is subjected to torque fluctuations in the retard direction, the operating oil in the advance hydraulic chamber is to be subjected to such pressure as to be pushed out of the advance hydraulic chamber or when the vane rotor is subjected to torque fluctuations in the advance direction, the operating oil in the retard hydraulic chamber is to be subjected to such pressure as to be pushed out of the retard hydraulic chamber. In consequence, in a low-rotation region where pressures supplied from a hydraulic supply source are low, even when a displacement angle of the cam shaft is designed to be advanced by supplying the hydraulic pressure to the advance hydraulic chamber, the vane rotor is, as shown in a dotted line of FIG. 3, pushed back in the retard direction due to the torque fluctuations. As a result, the response time to a target displacement angle of the vane rotor is longer.

In order to solve this problem, as shown in U.S. Pat. No. 6,763,791B2, a one-way valve is disposed in each of a hydraulic supply passage of an advance hydraulic chamber and a hydraulic supply passage of a retard hydraulic chamber for preventing reverse flow of operating oil from the advance hydraulic chamber or the retard hydraulic chamber. Thereby, as shown in a solid line of FIG. 3, it is considered that this one-way valve is adapted to prevent the vane rotor from being pushed back in the reverse direction to the direction of a target displacement angle during variable valve timing controlling, improving responsiveness of the variable valve timing control.

In the variable valve timing controller described in U.S. Pat. No. 6,763,791B2, the one-way valve is disposed in each of the hydraulic supply passage of the advance hydraulic chamber and the hydraulic supply passage of the retard hydraulic chamber (hydraulic introduction line) and also a returning line (hydraulic discharge line) is disposed in parallel to the hydraulic supply passage of each hydraulic chamber for bypassing the one-way valve. As a result, this controller provides a structure where a function as a line switching valve for opening/closing the returning line of each hydraulic chamber is united to a hydraulic control valve (spool-type electromagnetic valve) controlling the hydraulic pressure supplied to each hydraulic chamber. Further, a control current value of the hydraulic control valve is controlled to control the hydraulic pressure supplied to each hydraulic chamber and at the same time, to control the switching in opening/closing of the returning line of each hydraulic chamber. Hereby, when the hydraulic pressure in each hydraulic chamber is required to be released, this controller is adapted to release the hydraulic pressure through the returning line by opening the returning line of the corresponding hydraulic chamber.

In this variable valve timing controller, however, an armature in the hydraulic control valve is driven by an electric variable force solenoid to increase the entire length of the controller in the cam shaft direction, deteriorating the mounting properties.

The present applicant has proposed a variable valve timing controller having the structure where drain oil passages bypassing one-way valves are provided with drain switching valves disposed therein and driven by hydraulic pressures, and an electromagnetic type hydraulic switching valve for switching the hydraulic pressure driving each drain switching valve is disposed. Since in this structure, the drain switching valve can be small-sized and electrical wiring to the drain switching valve is not required, the drain switching valve together with the one-way valve can be downsized to be incorporated in a narrow space inside the variable valve timing controller. Further, since the hydraulic switching valve and the hydraulic control valve for controlling the hydraulic pressure supplied to each hydraulic chamber in the variable valve timing controller are not required to be mounted directly to the cam shaft, this variable valve timing controller has an advantage that the mounting properties thereof improve. It should be noted that the present applicant has further improved the aforementioned variable valve timing controller and has also proposed a variable valve timing controller having a structure where a single hydraulic control valve switches the hydraulic pressure driving each drain switching valve and controls the hydraulic pressure supplied to each hydraulic chamber in the variable valve timing controller.

It is found out during the developing process of the variable valve timing mechanism that it has the possibility that when an engine operates for a long term in an endurance test or the like, foreign matter is forced to be entered into a drain switching valve or a one-way valve or these valve bodies are stuck, so that the drain switching valve or the one-way valve does not operate normally (possibility that an advance/retard operation becomes abnormal). Since this abnormality deteriorates the engine performance, it is required to detect it as soon as possible to let a driver to be informed of it for repair.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a diagnosis system of a vane-type variable valve timing controller which can quickly detect abnormality in an advance/retard operation thereof during engine operating.

In order to achieve the above object, the present invention is provided with a one-way valve disposed in each of a hydraulic supply passage of an advance hydraulic chamber and a hydraulic supply passage of a retard hydraulic chamber in at least one of vane accommodating chambers for preventing reverse flow of operating oil from each hydraulic chamber, a drain oil passage disposed in parallel to the hydraulic supply passage of each hydraulic chamber for bypassing the one-way valve, a drain switching valve disposed in each drain oil passage and driven by hydraulic pressures and a hydraulic switching valve switching the hydraulic pressure driving each drain switching valve. During hold operating of holding a displacement angle of the variable valve timing controller (hereinafter, referred to as VTC displacement angle) to a target displacement angle, both drain switching valves in a side of the advance hydraulic chamber and a side of the retard hydraulic chamber are closed to effectively function both the one-way valves in the side of the advance hydraulic chamber and the side of the retard hydraulic chamber, controlling the hydraulic switching valve so as to prevent reverse flow of the operating oil from both the hydraulic chambers and also controlling a control current of the hydraulic control valve controlling the hydraulic pressure in the each hydraulic chamber to a predetermined holding current. During advance/retard operating of displacing the VTC displacement angle to the advance direction or the retard direction, the drain switching valve in either one of the advance hydraulic chamber side and the retard hydraulic chamber side is opened in accordance with the displacement direction to control the hydraulic switching valve so that either one of the one-way valves does not operate. Further, the control current of the hydraulic control valve is controlled to vary the hydraulic pressure in each hydraulic chamber, displacing the VTC displacement angle toward the target displacement angle. In addition, diagnosis means is adapted to determine presence/absence of abnormality in the advance/retard operation based upon a changing rate of the VTC displacement angle when a predetermined abnormality diagnosis execution condition is met during the advance/retard operating.

When the entire system is operating normally, during retard operating, the drain switching valve in the side of the advance hydraulic chamber is opened, making the operating oil in the advance hydraulic chamber be easily drained through the drain switching valve and at the same time, the drain switching valve in the side of the retard hydraulic chamber is closed to make the function of the one-way valve in the side of the retard hydraulic chamber be effected well, preventing reverse flow of the operating oil from the retard hydraulic chamber with the one-way valve, while performing control of filling the operating oil in the retard hydraulic chamber. Hereby, even at a low hydraulic pressure, coping with the torque fluctuations in the advance direction transmitted from the cam shaft, the reverse flow of the operating oil from the retard hydraulic chamber is prevented with the one-way valve and at the same time, the hydraulic pressure is efficiently supplied to the retard hydraulic chamber, improving the retard responsiveness.

In addition, during advance operating, the drain switching valve in the side of the retard hydraulic chamber is opened, making the operating oil in the retard hydraulic chamber be easily drained through the drain switching valve and the drain switching valve in the side of the advance hydraulic chamber is closed to make the function of the one-way valve in the side of the advance hydraulic chamber be effected well, preventing reverse flow of the operating oil from the advance hydraulic chamber with the one-way valve, while performing control of filling the operating oil in the advance hydraulic chamber. Hereby, even at a low hydraulic pressure, coping with the torque fluctuations in the retard direction transmitted from the cam shaft, the reverse flow of the operating oil from the advance hydraulic chamber is prevented with the one-way valve and at the same time, the hydraulic pressure is efficiently supplied to the advance hydraulic chamber, improving the advance responsiveness.

In consideration of such characteristic, the present invention determines whether or not responsiveness in an advance/retard operation is within a normal range based upon a changing rate of a VTC displacement angle during advance/retard operating to determine presence/absence of abnormality in the corresponding advance/retard operation, thereby enabling abnormality in the advance/retard operation during engine operating to be quickly detected.

According to the present invention, during hold operating, when a predetermined abnormality diagnosis execution condition is met, the holding current may be vibrated in a certain amplitude to determine presence/absence of abnormality in the drain switching valve and/or the one-way valve based upon a changing rate of the VTC displacement angle by the vibration of the holding current.

When both of the drain switching valves in the side of the advance hydraulic chamber and the side of the retard hydraulic chamber operate normally during hold operating, both of the drain switching valves close. Therefore, if both the one-way valves are normal, the reverse flow-preventing function of both the one-way valves can be effectively applied. However, when there occurs an open abnormality state where either one of the drain switching valves (or one-way valves) stops at a state of being opened, even during hold operating, either one of the drain switching valves (or one-way valves) is fixed at the state of being opened. Accordingly, when the holding current is vibrated in a certain amplitude during hold operating to determine a changing amount of the VTC displacement angle due to the vibration of the holding current, if both of the drain switching valves normally close and the function of the one-way valve is effectively applied, leak of the hydraulic pressure from both of the hydraulic chambers is effectively prevented with both of the one-way valves and therefore, a changing amount of the VTC displacement angle is reduced. When either one of the drain switching valves (or one-way valves) is at an open abnormality state, the hydraulic pressure in the hydraulic chamber at a side where the open abnormality occurs is leaked through the drain switching valve (or one-way valve) and reduced. In consequence, a balance in hydraulic pressure between both of the hydraulic chambers is off and it is hard to maintain the VTC displacement angle at a constant position, so that a changing amount of the VTC displacement angle increases. Accordingly, if the holding current is vibrated during hold operating as in the case of the present invention, the determination can be made as to presence/absence of abnormality in a drain switching valve and/or a one-way valve based upon whether or not the changing degree of the VTC displacement angle due to the vibration of the holding current is great. As a result, abnormality in the drain switching valve or the one-way valve can be quickly detected.

According to the diagnosis system of the present invention, when both of the drain switching valves (or one-way valves) in the side of the advance hydraulic chamber and in the side of the retard hydraulic chamber are simultaneously at an open abnormality state, it may be hard to detect the abnormality, but probability that both of the drain switching valves (or one-way valves) are simultaneously abnormal is extremely small as compared to the probability that either one of the drain switching valves (or one-way valves) is abnormal. Therefore, abnormality in most cases can be quickly detected by the abnormality diagnosis method of the present invention.

Further, according to the present invention, the determination may be made, based upon a changing amount of the VTC displacement angle within a certain period, as to occurrence of open abnormality where the drain switching valve and/or the one-way valve stops at a state of being opened during holding operating.

When both of the drain switching valves in the side of the advance hydraulic chamber and in the side of the retard hydraulic chamber operate normally during hold operating, both of the drain switching valves close. Therefore, if both of the one-way valves are normal, the reverse flow preventing function of both of the one-way valves can be effectively applied. However, when there occurs an open abnormality state where either one of the drain switching valves (one-way valves) stops at a state of being opened, even during hold operating either one of the drain switching valves (or one-way valves) is fixed at the state of being opened. Therefore, When either one of the drain switching valves (or one-way valves) is at an open abnormality state during hold operating, the hydraulic pressure in the hydraulic chamber at a side where the open abnormality occurs is leaked through the drain switching valve (or one-way valve) and reduced. In consequence, a balance in hydraulic pressure between both of the hydraulic chambers is off and it is hard to maintain the VTC displacement angle at a constant position, so that there occurs the phenomenon that a changing amount of the VTC displacement angle increases. Considering this characteristic, the present invention is designed, during hold operating, to determine whether or not open abnormality occurs in a drain switching valve and/or a one-way valve based upon the changing amount of the VTC displacement angle within a certain period. As a result, open abnormality in the drain switching valve or the one-way valve can be quickly detected.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram showing a variable valve timing controller and a hydraulic control circuit thereof. Example 1 of the present invention.

FIGS. 2A, 2B and 2C are diagrams each explaining a retard operation, a holding operation and an advance operation in the variable valve timing controller.

FIG. 3 is a characteristic diagram explaining a difference in VTC response rate at advance operating depending on presence/absence of a one-way valve.

FIG. 4 is a characteristic diagram showing one example of a response characteristic of the variable valve timing controller with a one-way valve.

FIG. 5 is a diagram explaining a relation between abnormality in an advance/retard operation and open abnormality/closed abnormality of a drain switching valve or a one-way valve.

FIG. 6 is a flow chart explaining the process order in an abnormality diagnosis routine.

FIG. 7 is a time chart explaining a behavior of an abnormality diagnosis process at a point when abnormality of an advance operation occurs.

FIG. 8 is a time chart explaining an abnormality diagnosis method in Example 2 of the present invention.

FIG. 9 is a flow chart explaining the process order in an abnormality diagnosis routine.

FIG. 10 is a flow chart explaining the process order in an abnormality diagnosis routine.

FIG. 11 is a flow chart explaining the process order in an abnormality diagnosis routine.

FIG. 12 is a flow chart explaining the process order in a dither correction duty calculation routine.

FIG. 13 is a diagram showing one example of a map of an increasing direction amplitude dizp of a dither in a hold duty.

FIG. 14 is a diagram showing one example of a map of a reducing direction amplitude dizm of a dither in a hold duty.

FIG. 15 is a diagram showing one example of a map of an amplitude direction switching time tmdiz of a dither in a hold duty.

FIG. 16 is a time chart explaining an abnormality diagnosis method in Example 3 of the present invention.

FIG. 17 is a time chart explaining an abnormality diagnosis method in Example 3 of the present invention.

FIG. 18 is a flow chart explaining the process order in an abnormality diagnosis routine in Example 3 of the present invention.

FIG. 19 is a flow chart explaining the process order in an abnormality diagnosis routine in Example 3 of the present invention.

FIG. 20 is a flow chart explaining the process order in an abnormality diagnosis routine in Example 3 of the present invention.

FIG. 21 is a time chart explaining an abnormality diagnosis method in Example 4 of the present invention.

FIG. 22 is a flow chart explaining the process order in an abnormality diagnosis routine in Example 4 of the present invention.

FIG. 23 is a flow chart explaining the process order in an abnormality diagnosis routine in Example 4 of the present invention.

FIG. 24 is a schematic diagram showing a variable valve timing controller and a hydraulic control circuit thereof in Example 5 of the present invention.

FIG. 25 is a schematic diagram showing a variable valve timing controller and a hydraulic control circuit thereof in Example 6 of the present invention.

DETAILED DESCRIPTION OF THE EXAMPLE EMBODIMENT Embodiment 1

First, a structure of a vane-type variable valve timing controller 11 will be explained with reference to FIG. 1. A housing 12 of the variable valve timing controller 11 is clamped and fixed to a sprocket rotatably supported at an outer periphery of a cam shaft in an intake side or an exhaust side (not shown) by bolts 13. In consequence, rotation of a crankshaft for an engine is transmitted through a timing chain to the sprocket and the housing 12 and the sprocket and the housing 12 rotate in a timed relation to the crankshaft. A vane rotor 14 is accommodated inside the housing 12 so as to rotate relative thereto and is clamped and fixed to one end of the camshaft by a bolt 15.

A plurality of vane accommodating chambers 16 for accommodating a plurality of vanes 17 at an outer periphery of the vane rotor 14 so as to rotate in the advance direction or the retard direction relative to the housing 12 are defined inside the housing 12 and each vane accommodating chamber 16 is divided into an advance hydraulic chamber 18 and a retard hydraulic chamber 19.

At a state where a hydraulic pressure beyond a predetermined pressure is supplied to the advance hydraulic chamber 18 and the retard hydraulic chamber 19, the vane 17 is held by the hydraulic pressures in the advance hydraulic chamber 18 and the retard hydraulic chamber 19 to transmit rotation of the housing 12 caused by rotation of the crank shaft to the vane rotor 14 through the hydraulic pressures, thereby rotating the cam shaft integrally with the vane rotor 14. During engine operating, the hydraulic pressures in the advance hydraulic chamber 18 and the retard hydraulic chamber 19 are controlled by a hydraulic control valve 21 to rotate the vane rotor 14 relative to the housing 12, thereby controlling a displacement angle of the cam shaft (cam shaft phase) to the crank shaft to vary valve timing of an intake valve (or exhaust valve).

In addition, stoppers 22 and 23 for controlling a relative rotational range of the vane rotor 14 to the housing 12 are formed at both side portions of either one of the vanes 17, and the maximum retard position and the maximum advance position of the displacement angle of the cam shaft (cam shaft phase) are restricted by the stoppers 22 and 23. In addition, either one of the vanes 17 is provided with a lock pin 24 disposed therein for locking a changing angle of the cam shaft at a certain lock position at engine stopping or the like. This lock pin 24 is inserted into a lock hole (not shown) disposed in the housing 12, causing the changing angle of the camshaft to be locked at a certain lock position. This lock position is set to a position suitable for engine startup (for example, substantially intermediate position within an adjustment possible range of a changing angle of the cam shaft).

Oil inside an oil pan 26 (operating oil) is supplied to a hydraulic control circuit of the variable valve timing controller 11 through the hydraulic control valve 21 by an oil pump 27. The hydraulic control circuit includes a hydraulic supply oil passage 28 supplying oil discharged from an advance pressure port of the hydraulic control valve 21 to a plurality of advance hydraulic chambers 18 and a hydraulic supply oil passage 29 supplying oil discharged from a retard pressure port of the hydraulic control valve 21 to a plurality of retard hydraulic chambers 19.

Further, One-way valves 30 and 31 are disposed in the hydraulic supply oil passage 28 of the advance hydraulic chamber 18 and the hydraulic supply oil passage 29 of the retard hydraulic chamber 19 for preventing reverse flow of the operating oil from the respective chambers 18 and 19. In the present embodiment, the one-way valves 30 and 31 are disposed in the hydraulic control oil passages 28 and 29 of the advance hydraulic chamber 18 and the retard hydraulic chamber 19 in the single vane accommodating chamber 16 only.

The one-way valves 30 and 31 may be disposed in the hydraulic control oil passages 28 and 29 of the advance hydraulic chamber 18 and the retard hydraulic chamber 19 in each of a plurality of the vane accommodating chambers 16 without mentioning.

Drain oil passage 32 and 33 for bypassing the one-way valves 30 and 31 respectively are disposed in parallel in the hydraulic supply oil passages 28 and 29 of the respective chambers 18 and 19, and drain switching valves 34 and 35 are disposed in the drain oil passages 32 and 33 respectively. The drain switching valves 34 and 35 respectively are formed of spool valves driven in a closing direction by hydraulic pressure (pilot pressure) supplied from the hydraulic control valve 21. When the hydraulic pressure is not applied, the drain switching valves 34 and 35 are held in an opening position. When the drain switching valves 34 and 35 are opened, the drain oil passages 32 and 33 are opened, causing functions of the one-way valves 30 and 31 to be stopped. When the drain switching valves 34 and 35 are closed, the drain oil passages 32 and 33 are closed, causing functions of the one-way valves 30 and 31 to be effectively performed. Therefore, the reverse flow of the oil from the hydraulic chambers 18 and 19 is prevented, maintaining the hydraulic pressures in the hydraulic chambers 18 and 19.

The drain switching valves 34 and 35 respectively do not require electrical wiring and therefore, are downsized to be incorporated in the vane rotor 14 inside the variable valve timing controller 11, together with the one-way valves 30 and 31. In consequence, the drain switching valves 34 and 35 are located near the hydraulic chambers 18 and 19 respectively and are adapted to open/close the respective drain oil passages 32 and 33 near the respective hydraulic chambers 18 and 19 at advance/retard operating in good response.

Further, in the present embodiment, considering that the entire variable valve timing controller 11 rotates along with rotation of the crank shaft during engine operating to apply a rotational centrifugal force to the respective drain switching valves 34 and 35, a mounting direction of each of the drain switching valves 34 and 35 to the vane rotor 14 is set in such a manner as to exert the rotational centrifugal force in the opening direction of the valve body. Thereby, in a region of a high-rotation side where an engine rotational speed is more than a predetermined value, the drain switching valves respectively are forcibly opened due to the rotational centrifugal force all the time regardless of the control hydraulic pressures in the drain switching valves 34 and 35 respectively, causing the functions of the respective one-way valves 30 and 31 to be stopped. As a result, the present embodiment is adapted to be capable of using, in a region of the high-rotation side, the same control program as in the conventional example without the one-way valves 30 and 31.

On the other hand, the hydraulic control valve 21 is formed of a spool valve driven by a linear solenoid 36, where an advance/retard hydraulic control valve 37 controlling the hydraulic pressures supplied to the advance hydraulic chamber 18 and the retard hydraulic chamber 19 is integral with the a drain switching control valve 38 switching the hydraulic pressure driving the drain switching valves 34 and 35 respectively. A current value (control duty) supplied to the linear solenoid 36 of the hydraulic control valve 21 is controlled by an engine control circuit (hereinafter referred to as “ECU”) 43.

The ECU 43 calculates actual valve timing (actual displacement angle) of the intake valve (exhaust valve) based upon output signals of a crank angle sensor 44 and a cam angle sensor 45 and also calculates target valve timing (target displacement angle) of the intake valve (exhaust valve) based upon outputs of various sensors such as an intake pressure sensor and a water temperature sensor for detecting an engine operating condition. In addition, the ECU 43 performs feedback control (or feedforward control) of a control current value of the hydraulic control valve 21 in the variable valve timing controller 11 so that the actual valve timing is equal to the target valve timing. Thereby, the hydraulic pressures in the advance hydraulic chamber 18 and the retard hydraulic chamber 19 are controlled to rotate the vane rotor 14 relative to the housing 12, causing a displacement angle of the cam shaft to be varied for making the actual valve timing be equal to the target valve timing.

Here, when the intake valve or the exhaust valve is opened/closed during engine operating, the torque fluctuation the cam shaft receives from the intake valve or the exhaust valve is transmitted to the vane rotor 14, causing the torque fluctuation in the retard direction and in the advance direction to be exerted on the vane rotor 14. In consequence; when the vane rotor 14 is subjected to the torque fluctuation in the retard direction, the operating oil in the advance hydraulic chamber 18 receives the pressure to be pushed out of the advance hydraulic chamber 18 and on the other hand, when the vane rotor 14 is subjected to the torque fluctuation in the advance direction, the operating oil in the retard hydraulic chamber 19 receives the pressure to be pushed out of the retard hydraulic chamber 19. Therefore, in a low-rotation region where a discharge hydraulic pressure of the oil pump 27 as a hydraulic supply source is low, without the one-way valves 30 and 31, even if the hydraulic pressure is designed to be supplied to the advance hydraulic chamber 18 to advance a displacement angle of the cam shaft, as shown in a dotted line of FIG. 3, the vane rotor 14 is pushed back in the retard direction due to the torque fluctuation, raising the problem that the response time until the vane rotor 14 reaches a target displacement angle is longer.

On the other hand, in the present embodiment, the one-way valves 30 and 31 are disposed in the hydraulic supply oil passage 28 of the advance hydraulic chamber 18 and the hydraulic supply oil passage 29 of the retard hydraulic chamber 19 for preventing reverse flow of the operating oil from the respective chambers 18 and 19. Further, the drain oil passage 32 and 33 for bypassing the one-way valves 30 and 31 respectively are disposed in parallel in the hydraulic supply oil passages 28 and 29 of the respective chambers 18 and 19, and drain switching valves 34 and 35 are disposed in the drain oil passages 32 and 33 respectively. As a result, as shown in FIGS. 2A, 2B and 2C, the hydraulic pressures in the chambers 18 and 19 respectively are controlled in response to a retard operation, a holding operation and an advance operation as follows.

[Retard Operation]

As shown in FIG. 2A, during retard operating where the actual valve timing is retarded toward the target valve timing in the retard side, the hydraulic pressure is added to the drain switching valve 34 in the advance hydraulic chamber 18 from the hydraulic control valve 21 to open the drain switching valve 34 in the advance hydraulic chamber 18, creating the state where the one-way valve 30 in the advance hydraulic chamber 18 does not function. Further, the hydraulic supply to the drain switching valve 35 in the retard hydraulic chamber 19 is stopped to close the drain switching valve 35 in the retard hydraulic chamber 19, creating the state where the one-way valve 31 in the retard hydraulic chamber 19 functions. In consequence, even at a low hydraulic pressure, upon occurrence of the torque fluctuation in the advance direction of the vane rotor 14, the reverse flow of oil from retard hydraulic chamber 19 is prevented with the one-way valve 31, while efficiently supplying the hydraulic pressure to the retard hydraulic chamber 19, thereby to improve retard responsiveness.

It should be noted that in the present embodiment, in a region of a high-rotation side where an engine rotational speed is more than a predetermined value, the drain switching valves 34 and 35 respectively are forcibly opened due to the rotational centrifugal force all the time regardless of the control hydraulic pressure in the drain switching valves 34 and 35 respectively, creating the state where the functions of the respective one-way valves 30 and 31 do not work. As a result, in a region of the high-rotation side, even at retard operating, the drain switching valves 34 and 35 respectively are forcibly opened due to the rotational centrifugal force all the time, causing the functions of the respective one-way valves 30 and 31 to be stopped. However, since in a region of the high-rotation side, the discharge hydraulic pressure of the oil pump 27 can be sufficiently high to supply a sufficiently high hydraulic pressure to the retard hydraulic chamber 19, the retard responsiveness is not deteriorated.

[Holding Operation]

As shown in FIG. 2B, during holding operating where the actual valve timing is held to the target valve timing, the hydraulic supply to both of the drain switching valves 34 and 35 in the advance hydraulic chamber 18 and in the retard hydraulic chamber 19 is stopped to close the drain switching valves 34 and 35, creating the state where the one-way valves 30 and 31 in the advance hydraulic chamber 18 and in the retard hydraulic chamber 19 function. In this state, even if the torque fluctuations in the retard direction and in the advance direction are applied to the vane rotor 14 due to the torque fluctuations the cam shaft receives from the intake valve or the exhaust valve, the reverse flow of oil from both of the advance hydraulic chamber 18 and the retard hydraulic chamber 19 is prevented with the one-way valve 31 to prevent reduction in the hydraulic pressures holding the vane 17 from both side thereof, thereby to improve holding stability.

In this holding operation also, in a region of a high-rotation side, the drain switching valves 34 and 35 respectively are forcibly opened due to the rotational centrifugal force, causing the state where the functions of the respective one-way valves 30 and 31 are stopped, but since in a region of the high-rotation side, the discharge hydraulic pressure of the oil pump 27 can be sufficiently high to supply a sufficiently high hydraulic pressure to both of the advance hydraulic chamber 18 and the retard hydraulic chamber 19, the holding stability is not reduced.

[Advance Operation]

As shown in FIG. 2C, during advance operating where the actual valve timing is advanced toward the target valve timing in the advance side, the hydraulic pressure supply to the drain switching valve 34 in the advance hydraulic chamber 18 is stopped to close the drain switching valve 34 in the advance hydraulic chamber 18, causing the state where the one-way valve 30 in the advance hydraulic chamber 18 functions. Further, the hydraulic pressure from the hydraulic control valve 21 is applied to the drain switching valve 35 in the retard hydraulic chamber 19 is added to open the drain switching valve 35 in the retard hydraulic chamber 19, creating the state where the one-way valve 31 in the retard hydraulic chamber 19 does not function. In consequence, even at a low hydraulic pressure, the reverse flow of oil from the advance hydraulic chamber 18 upon occurrence of the torque fluctuation in the retard direction of the vane rotor 14 is prevented with the one-way valve 30, while efficiently supplying the hydraulic pressure to the advance hydraulic chamber 18, thereby to improve advance responsiveness.

In this advance operation also, in a region of a high-rotation side, the drain switching valves 34 and 35 respectively are forcibly opened due to the rotational centrifugal force, causing the state where the functions of the respective one-way valves 30 and 31 are stopped, but since in a region of the high-rotation side, the discharge hydraulic pressure of the oil pump 27 can be sufficiently high to supply a sufficiently high hydraulic pressure to the advance hydraulic chamber 18, the advance responsiveness is not deteriorated.

Next, the response characteristic of the variable valve timing controller 11 (hereinafter referred to as “VTC response characteristic”) will be explained with reference to FIG. 4. FIG. 4 shows one example of a response characteristic obtained by measuring a relation between a control current value of the hydraulic control valve 21 (hereinafter, referred to as “OCV current value”) and a response rate of the variable valve timing controller 11 (hereinafter, referred to as “VTC response rate”).

In Embodiment 1, since the one-way valves 30 and 31 and the drain switching valves 34 and 35 are disposed in both of the advance hydraulic chamber 18 and the retard hydraulic chamber 19, a VTC response rate does not change linearly to a change of an OCV current value and opening/closing of the drain switching valves 34 and 35 is switched, causing the VTC rate to rapidly change at two locations. In the VTC response characteristic of FIG. 4, the rapidly changing point of the VTC response rate at the retard side is a point where the drain switching valve 34 in the advance hydraulic chamber 18 switches from closing state to opening state, and the rapidly changing point of the VTC response rate at the advance side is a point where the drain switching valve 35 in the retard hydraulic chamber 19 switches from closing state to opening state. The holding operation is made in a region where a grade of a VTC response rate change between the rapidly changing point of the VTC response rate at the retard side and the rapidly changing point of the VTC response rate at the advance side is small.

Here, when the use term is long, foreign materials are entered into the drain switching valves 34 and 35 or the one-way valves 30 and 31 or these valve bodies are stuck, possibly producing “an open abnormality” state where the drain switching valves 34 and 35 or the one-way valves 30 and 31 stop at a state of being opened or “a closed abnormality” state where the drain switching valves 34 and 35 or the one-way valves 30 and 31 stop at a state of being closed. Such open abnormality state is the cause of deteriorating the engine performance and therefore, it is required to detect it as soon as possible and inform a driver of it for repair.

Therefore, the present embodiment is adapted to determine whether or not the responsiveness of the advance/retard operation is within a normal range based upon a changing rate of the VTC displacement angle during advance/retard operating, determining presence/absence of abnormality in the advance/retard operation. Here, it is considered that the causes of generating abnormality of an advance/retard operation include a case of abnormality in the hydraulic control 21 and a case of abnormality in the drain switching valves 34 and 35 or the one-way valves 30 and 31. Hereinafter, the causes of generation abnormality in the advance/retard operation will be examined.

[Cause of Generating Abnormality in an Advance Operation]

In a case where the hydraulic control valve 21 operates normally, as causes of generating abnormality in the advance operation, as shown in FIG. 5, the next four abnormal modes (or the combination) are considered.

(A1) Closed Abnormality in the Drain Switching Valve 35 at the Side of the Retard Hydraulic Chamber 19

During advance operating, there is performed control of draining oil in the retard hydraulic chamber 19 is drained and at the same time, filling oil into the advance hydraulic chamber 18. However, when the drain switching valve 35 at the side of the retard hydraulic chamber 19 is in a closed abnormality state, it is hard to drain the oil of the retard hydraulic chamber 19. Therefore, it is hard to fill oil into the advance hydraulic chamber 18, causing a changing rate of the VTC displacement angle at advance operating to be excessively slow.

(A2) Closed Abnormality in the One-Way Valve 30 at the Side of the Advance Hydraulic Chamber 18

Since during advance operating, the drain switching valve 34 at the side of the advance hydraulic chamber 18 is closed, when the one-way valve 30 at the side of the advance hydraulic chamber 18 is in a closed abnormality state, the oil can not be filled into the advance hydraulic chamber 18 at all, causing a changing rate of the VTC displacement angle at advance operating to be excessively slow.

(A3) Open Abnormality in the Drain Switching Valve 34 at the Side of the Advance Hydraulic Chamber 18

When during advance operating, the drain switching valve 35 at the side of the advance hydraulic chamber 18 is in an open abnormality state, the hydraulic pressure in the advance hydraulic chamber 18 tends to easily flow back through the drain switching valve 34 due to the torque fluctuation in the retard direction transmitted from the cam shaft, causing a changing rate of the VTC displacement angle at advance operating to be slow.

(A4) Open Abnormality in the One-Way Valve 30 at the Side of the Advance Hydraulic Chamber 18

When during advance operating, the one-way valve 30 at the side of the advance hydraulic chamber 18 is in an open abnormality state, the hydraulic pressure in the advance hydraulic chamber 18 tends to easily flow back through the one-way valve 30 due to the torque fluctuation in the retard direction transmitted from the cam shaft, causing a changing rate of the VTC displacement angle at advance operating to be slow.

[Cause of Generating Abnormality in a Retard Operation]

In a case where the hydraulic control valve 21 operates normally, as causes of generating abnormality in the retard operation, as shown in FIG. 5, the next four abnormal modes (or the combination) are considered.

(B1) Closed Abnormality in the Drain Switching Valve 34 at the Side of the Advance Hydraulic Chamber 18

During retard operating, there is performed control of draining oil in the advance hydraulic chamber 18 and at the same time, filling oil into the retard hydraulic chamber 19. However, when the drain switching valve 34 at the side of the advance hydraulic chamber 18 is in a closed abnormality state, it is hard to drain the oil in the advance hydraulic chamber 18. Therefore, it is hard to fill oil into the retard hydraulic chamber 19, causing a changing rate of the VTC displacement angle at retard operating to be excessively slow.

(B2) Closed Abnormality in the One-Way Valve 31 at the Side of the Retard Hydraulic Chamber 19

Since during retard operating, the drain switching valve 35 at the side of the retard hydraulic chamber 19 is closed, when the one-way valve 31 at the side of the retard hydraulic chamber 19 is in a closed abnormality state, the oil can not be filled into the retard hydraulic chamber 19 at all, causing a changing rate of the VTC displacement angle at retard operating to be excessively slow.

(B3) Open Abnormality in the Drain Switching Valve 35 at the Side of the Retard Hydraulic Chamber 19

When during retard operating, the drain switching valve 35 at the side of the retard hydraulic chamber 19 is in an open abnormality state, the oil in the retard hydraulic chamber 19 tends to easily flow back through the drain switching valve 35 due to the torque fluctuation in the advance direction transmitted from the cam shaft, causing a changing rate of the VTC displacement angle at retard operating to be slow.

(B4) Open Abnormality in the One-Way Valve 31 at the Side of the Retard Hydraulic Chamber 19

When during retard operating, the one-way valve 31 at the side of the retard hydraulic chamber 19 is in an open abnormality state, the oil in the retard hydraulic chamber 19 tends to easily flow back through the one-way valve 31 due to the torque fluctuation in the advance direction transmitted from the cam shaft, causing a changing rate of the VTC displacement angle at retard operating to be slow.

Using the aforementioned determination criteria, the open abnormality or the closed abnormality in the drain switching valves 34 and 35 or the one-way valves 30 and 31 can be determined based upon the changing rate of the VTC displacement angle.

In the present embodiment, the ECU 43 executes an abnormality diagnosis routine in FIG. 6. Thereby, it is determined whether or not the responsiveness of an advance/retard operation is within a normal range based upon a changing rate of the VTC displacement angle during advance/retard operating, determining presence/absence in abnormality in the advance/retard operation as follows.

The abnormality diagnosis routine in FIG. 6 is executed at every calculation timing of an engine rotational speed during engine operating (for example, each of 180 degrees in a case of a four-cylinder engine). When the present routine is activated, first at step 101, it is determined whether or not the VTC displacement angle is in the middle of changing (in the middle of advance or retard operating). When the VTC displacement angle is not in the middle of changing, the present routine ends without execution of the subsequent processes.

On the other hand, when the VTC displacement angle is determined at step 101 to be in the middle of changing (during advance or retard operating), the process goes to step 102, wherein it is determined whether or not the abnormality diagnosis execution condition is met based upon, for example, whether or not the next conditions (1) to (3) are all satisfied.

-   -   (1) An engine rotational speed is in a low rotation region less         than a predetermined rotational speed Ne1 (however, more than a         predetermined rotational speed Ne2 where the discharge hydraulic         pressure of the oil pump 27 is stable)     -   (2) A deviation between a VTC displacement angle and a target         displacement angle is more than a predetermined value.     -   (3) In a certain time elapse after the target displacement angle         has changed.         Here, the reason for the condition (1) is that in a low rotation         region where the engine rotational speed is less than a         predetermined rotational speed Ne1, the hydraulic pressure         supplied from the oil pump 27 as the hydraulic supply source is         low and therefore, when the drain switching valves 34 and 35 or         the one-way valves 30 and 31 do not operate normally, the         responsiveness at advance/retard operating tends to         significantly deteriorate, easily detecting the abnormality. In         addition, this is because there is a case where in a region of a         high rotation side, even in a case of the operation in either         one of the advance and retard directions, both of the drain         switching valves 34 and 35 in the side of the advance hydraulic         chamber 18 and in the side of the retard hydraulic chamber 19         are adapted to be automatically opened by a rotational         centrifugal force or the like.

However, when the engine rotational speed becomes excessively low, the discharge hydraulic pressure of the oil pump 27 becomes excessively low to reduce the responsiveness in the advance/retard operation. Therefore, it is preferable to set the requirement that the engine rotational speed is more than a predetermined rotational speed Ne2 where the discharge hydraulic pressure of the oil pump 27 can be stably obtained. Besides, since the responsiveness in the advance/retard operation has also a relation with viscosity of oil (oil temperature), the requirement that the oil temperature or temperature information (for example, engine cooling water temperature) correlating thereto is more than a predetermined temperature may be used as the abnormality diagnosis execution condition.

In addition, the condition (2) is made in consideration of the characteristic of the VTC displacement angle feedback control that when the a deviation between a VTC displacement angle and a target displacement angle is smaller, a changing rate of the VTC displacement is slower and is the condition required for a changing rate of the VTC displacement angle at normal operation time to be greater than a threshold value to be described later.

In addition, the condition (3) is made, in consideration of the response delay by which a changing rate of the VTC displacement angle increases with a change of a target displacement angle, for determining a changing rate of the VTC displacement after an elapse of a predetermined time corresponding to the maximum allowance response delay time at a normal operation time until the changing rate exceeds the determination threshold value to be described later after the target displacement angle has changed.

When even one of these three conditions (1) to (3) is not satisfied, the abnormality diagnosis execution condition is to be not met and the present routine ends without performing the subsequent processes.

On the other hand, when the three conditions (1) to (3) are all satisfied, it is determined that the abnormality diagnosis execution condition is met and the process goes to step 103, wherein an abnormality diagnosis execution flag is set as “1” meaning “during abnormality diagnosis executing”. After that, the process goes to step 104, wherein it is determined whether the present VTC operating state is an advance operation or a retard operation. As a result, when it is determined that it is the advance operation, the process goes to step 105, wherein it is determined whether or not the hydraulic control valve 21 is normal by the other abnormality diagnosis function. If it is determined that the hydraulic control valve 21 is abnormal, the present routine ends without performing the subsequent processes.

When at step 105, it is determined that the hydraulic control valve 21 is normal, the process goes to step 106, wherein it is determined whether or not a changing rate in the advance direction of the VTC displacement angle (hereinafter referred to as “advance rate”) exceeds a predetermined determination threshold value. When the advance rate exceeds a predetermined determination threshold value, the process goes to step 107, wherein an advance operation abnormality determination flag is set as “0” which means that the advance operation is normal, and the present routine ends.

On the other hand, when at step 106, it is determined that the advance rate is less than a determination threshold value, the process goes to step 108, wherein there is counted up an advance operation abnormality counter for measuring continuing time of the state where the advance rate remains to be is less than the determination threshold value. In addition, at next step 109, it is determined whether or not the measurement time of the advance operation abnormality counter (continuing time of the state where the advance rate is less than the determination threshold value) exceeds a predetermined time T. When it is determined that the measurement time of the advance operation abnormality counter is less than the predetermined time T, the present routine ends as it is.

On the other hand, at step 109 when it is determined that the measurement time of the advance operation abnormality counter exceeds the predetermined time T, it is determined that the advance operation is abnormal, the process goes to step 110, wherein the advance operation abnormality determination flag is set as “1” which means that the advance operation is abnormal, and the present routine ends.

In a case where it is thus determined that the advance operation is abnormal, it is determined that the cause of generating the abnormality in the advance operation is, as shown in FIG. 5, any of (A1) Closed abnormality in the drain switching valve 35 at the side of the retard hydraulic chamber 19, (A2) Closed abnormality in the one-way valve 30 at the side of the advance hydraulic chamber 18, (A3) Open abnormality in the drain switching valve 34 at the side of the advance hydraulic chamber 18, and (A4) Open abnormality in the one-way valve 30 at the side of the advance hydraulic chamber 18.

In addition, at step 104, when it is determined that the VTC operation state is the retard operation, the process goes to step 115, wherein it is determined whether or not the hydraulic control valve 21 is normal by the other abnormality diagnosis function. If it is determined that the hydraulic control valve 21 is abnormal, the present routine ends without performing the subsequent processes.

When at step 115, it is determined that the hydraulic control valve 21 is normal, the process goes to step 116, wherein it is determined whether or not a changing rate in the retard direction of the VTC displacement angle (hereinafter referred to as “retard rate”) exceeds a predetermined determination threshold value. When the retard rate exceeds a predetermined determination threshold value, the process goes to step 117, wherein a retard operation abnormality determination flag is set as “0” which means that the retard operation is normal, and the present routine ends.

On the other hand, when at step 116, it is determined that the retard rate is less than a determination threshold value, the process goes to step 118, wherein there is counted up a retard operation abnormality counter for measuring continuing time of the state where the retard rate remains to be is less than the determination threshold value. In addition, at step 119, it is determined whether or not the measurement time of the retard operation abnormality counter (continuing time of the state where the retard rate remains to be is less than the determination threshold value) exceeds a predetermined time T. When it is determined that the measurement time of the retard operation abnormality counter is less than the predetermined time T, the present routine ends as it is.

On the other hand, at step 119, when it is determined that the measurement time of the retard operation abnormality counter is less than the predetermined time T, it is determined that the retard operation is abnormal, and the process goes to step 120, wherein the retard operation abnormality determination flag is set as “1” which means that the retard operation is abnormal, and the present routine ends.

In a case where it is thus determined that the retard operation is abnormal, it is determined that the cause of generating the abnormality in the retard operation is, as shown in FIG. 5, any of (B1) Closed abnormality in the drain switching valve 34 at the side of the advance hydraulic chamber 18, (B2) Closed abnormality in the one-way valve 31 at the side of the retard hydraulic chamber 19, (B3) Open abnormality in the drain switching valve 35 at the side of the retard hydraulic chamber 19, and (B4) Open abnormality in the one-way valve 31 at the side of the retard hydraulic chamber 19.

One example of the abnormality diagnosis in the present embodiment is shown in a time chart of FIG. 7. In the example of FIG. 7, at time t1 a target displacement angle changes in the advance direction and according to it, a VTC displacement angle is feedback-controlled in such a manner as to change in the advance direction.

At time t2 where a predetermined time elapses after the change of the target displacement angle and the abnormality diagnosis execution condition is met, the abnormality diagnosis execution flag is set as “1” and the abnormality diagnosis starts. During executing the abnormality diagnosis, the advance operation abnormality counter measures continuing time of the state where the retard rate remains to be less than the determination threshold value and at time t3 where the measurement time of the advance operation abnormality counter (continuing time of the state where the advance rate remains to be less than the determination threshold value) exceeds a predetermined time T, it is determined that advance operation is abnormal, and the advance operation abnormality determination flag is set as “1” which means that the advance operation is abnormal.

According to the present embodiment explained above, it is determined whether or not the responsiveness of an advance/retard operation is within a normal range based upon a changing rate of the VTC displacement angle during advance/retard operating, thus determining presence/absence in abnormality in the advance/retard operation. Therefore, during engine operating, abnormality in the advance/retard operation, finally the drain switching valves 34 and 35 or the one-way valves 30 and 31 can be quickly detected.

It should be noted that a hydraulic switching valve for switching the hydraulic pressure driving the drain switching valves 34 and 35 may be separated from the hydraulic control valve 21, but the present embodiment is so structured that the hydraulic switching valve is integral with the hydraulic control valve 21, and therefore, has an advantage of being capable of meeting the requirements such as reduction in the number of component parts, reduction in costs and downsizing.

Besides, the present invention may alter the structure of the variable valve timing controller 11 as needed and can make various modifications within the scope of the technical spirit thereof.

Embodiment 2

Embodiment 2 detects abnormality by using the following method, considering that in a region of a high-rotation side where an engine rotational speed is more than a predetermined value, the drain switching valves 34 and 35 respectively are forcibly opened due to the rotational centrifugal force all the time regardless of the control hydraulic pressure in the drain switching valves 34 and 35 respectively, creating the state where the functions of the respective one-way valves 30 and 31 do not work.

[Abnormality Diagnosis in a Region at a Low Rotation Side]

During holding operating, in a region of a low rotation side less than a predetermined rotational speed where the drain switching valves 34 and 35 of both the sides are closed if they are normal, as shown in FIG. 8, the holding current (hold duty) of the hydraulic control valve 21 is vibrated (dither) in a predetermined amplitude/cycle to determine a changing degree of the VTC displacement angle by the vibration of the holding current. In addition, occurrence of an open abnormality state where the drain switching valve 34 and/or the one-way valve 30 at the side of the advance hydraulic chamber 18 stop at a state of being opened is determined based upon whether or not the changing degree of the VTC displacement angle exceeds a predetermined abnormality determination threshold value and increases in the retard direction.

In a case of performing the holding operation at a region of the low rotation side, when the drain switching valves 34 and 35 at both the sides of the advance hydraulic chamber 18 and at the side of the retard hydraulic chamber 19 operate normally, the drain switching valves 34 and 35 at both the sides close. Therefore, when the drain switching valves 34 and 35 at both the sides are normal, the reverse flow prevention functions of the drain switching valves 34 and 35 at both the sides can be effectively performed. However, when the drain switching valve 34 and/or the one-way valve 30 at the side of the advance hydraulic chamber 18 are in an open abnormality state, the hydraulic pressure in the advance hydraulic chamber 18 where the open abnormality state is occurring is leaked through the drain switching valve 34 or the one-way valve 30 and is reduced. Therefore, the hydraulic pressure in the retard hydraulic chamber 19 is greater than the hydraulic pressure in the advance hydraulic chamber 18, creating the phenomenon that the VTC displacement angle displaces in the advance direction. Embodiment 2 uses this characteristic to detect an open abnormality state of the drain switching valve 34 and/or the one-way valve 30 at the side of the advance hydraulic chamber 18 based upon whether or not the changing degree of the VTC displacement angle exceeds a predetermined abnormality determination threshold value and increases in the retard direction.

Likewise, occurrence of an open abnormality state where the drain switching valve 35 and/or the one-way valve 31 at the side of the retard hydraulic chamber 19 do not move at a state of being opened is determined based upon whether or not the changing degree of the VTC displacement angle by vibration of the holding current exceeds a predetermined abnormality determination threshold value and increases in the advance direction. This is made based upon the following phenomenon. When the drain switching valve 35 and/or the one-way valve 31 at the side of the retard hydraulic chamber 19 are in an open abnormality state, the hydraulic pressure in the retard hydraulic chamber 19 where the open abnormality state is occurring is leaked through the drain switching valve 35 or the one-way valve 31 and is reduced. Therefore, the hydraulic pressure in the advance hydraulic chamber 18 is greater than the hydraulic pressure in the retard hydraulic chamber 19, creating the phenomenon that the VTC displacement angle displaces in the retard direction. Embodiment 2 uses this characteristic to detect an open abnormality state of the drain switching valve 35 and/or the one-way valve 31 at the side of the retard hydraulic chamber 19.

[Abnormality Diagnosis in a Region at a High Rotation Side]

During holding operating, in a region of a high rotation side where the drain switching valves 34 and 35 at both the sides are forcibly opened by a rotational centrifugal force if they are normal, creating the state where the functions of the one-way valves 30 and 31 at both the sides are not performed, the holding current (hold duty) of the hydraulic control valve 21 is vibrated (dither) in a predetermined amplitude/cycle to determine a changing degree of the VTC displacement angle by the vibration of the holding current as in the case of a region of a low rotation side. In addition, occurrence of a closed abnormality state where the drain switching valve 34 at the side of the advance hydraulic chamber 18 stops at a state of being closed is determined based upon whether or not the changing degree of the VTC displacement angle exceeds a predetermined abnormality determination threshold value and increases in the advance direction.

In a case of performing the holding operation at a region of the high rotation side, when the drain switching valves 34 and 35 at both the sides of the advance hydraulic chamber 18 and the retard hydraulic chamber 19 operate normally, the drain switching valves 34 and 35 at both the sides are forcibly opened by a rotational centrifugal force. However, when the drain switching valve 34 at the side of the advance hydraulic chamber 18 is in a closed abnormality state, the hydraulic pressure in the advance hydraulic chamber 18 where the closed abnormality state is occurring relatively increases by the vibration of the holding current. Therefore, the hydraulic pressure in the advance hydraulic chamber 18 is greater than the hydraulic pressure in the retard hydraulic chamber 19, creating the phenomenon that the VTC displacement angle displaces in the advance direction. Embodiment 2 uses this characteristic to detect a closed abnormality state of the drain switching valve 34 at the side of the advance hydraulic chamber 18 based upon whether or not the changing degree of the VTC displacement angle exceeds a predetermined abnormality determination threshold value and increases in the advance direction.

Likewise, occurrence of a closed abnormality state where the drain switching valve 35 at the side of the retard hydraulic chamber 19 does not move at a state of being closed is determined based upon whether or not the changing degree of the VTC displacement angle exceeds a predetermined abnormality determination threshold value and increases in the retard direction. This is made based upon the following phenomenon. When the drain switching valve 35 at the side of the retard hydraulic chamber 19 is in a closed abnormality state, the hydraulic pressure in the retard hydraulic chamber 19 where the closed abnormality state is occurring relatively increases by vibration of the holding current. Therefore, the hydraulic pressure in the retard hydraulic chamber 19 is greater than the hydraulic pressure in the advance hydraulic chamber 18, creating the phenomenon that the VTC displacement angle displaces in the retard direction. Embodiment 2 uses this characteristic to detect a closed abnormality state of the drain switching valve 35 at the side of the retard hydraulic chamber 19.

In addition, in the present embodiment, the amplitude and the cycle of the vibration (dither) of the holding current during abnormality diagnosis execution period are set in such a manner that a changing degree of the VTC displacement angle at a normal operation state is within a region of an allowance changing amount of the VTC displacement angle during usual holding operating. In this case, the holding operation is made in a region where a grade of a VTC response rate change between a VTC response rate rapid changing point at the retard side and a VTC response rate rapid changing point at the advance side is small and the amplitude of the holding current is set not to exceed the VTC response rate rapid changing point at the retard side and the VTC response rate rapid changing point at the advance side. In this way, in a case where the drain switching valves 34 and 35 at both the sides are normal, a changing amount of the VTC displacement angle during holding operating is made within a usual allowance range even during the vibration period of the holding current, enabling an abnormality diagnosis without adverse influence on the engine performance.

In this case, the amplitude of the holding current may be set in such a manner that the increasing direction is equal to the decreasing direction, but considering the characteristic that the hydraulic pressure in the advance hydraulic chamber 18 easier leaks than the hydraulic pressure in the retard hydraulic chamber 19 due to the structure of the vane-type variable valve timing controller 11, the amplitude of the vibration of the holding current is set so that an increasing direction amplitude (advance direction amplitude) of the holding current is slightly greater than a decreasing direction amplitude (retard direction amplitude) thereof in order that a VTC displacement angle changing amount of the increasing direction amplitude (advance direction amplitude) of the holding current is substantially the same as the decreasing direction amplitude (retard direction amplitude) thereof (refer to FIGS. 13 and 14). In this way, it is possible to effectively reduce the fluctuation of the VTC displacement angle during the vibration period of the holding current.

In addition, the present embodiment sets a cycle (dither cycle) of vibration of the holding current close to the minimum time in which the hydraulic pressure can be transmitted to each hydraulic chamber 18 and 19 in the increasing direction amplitude and the decreasing direction amplitude of the holding current in consideration of a delay of a hydraulic transmission system to the hydraulic chambers 18 and 19 respectively. In this way, the VTC displacement angle changing amount at a normal operation state is reduced and at the same time, the VTC displacement angle changing amount at an abnormal operation state can be increased. In consequence, a difference in VTC displacement angle changing amount between at a normal operation state and at an abnormal operation state is clarified, making it possible to easily detect the abnormality.

In addition, considering that there occurs a delay from a point of holding operation start until a point where the VTC displacement angle is stably held, the present embodiment, as shown in FIG. 8, starts vibration of the holding current after a predetermined period corresponding to the delay has elapsed from the holding operation start and is adapted to perform an abnormality diagnosis by making the vibration of the holding current for a predetermined period. This prevents erroneous determination that the fluctuation of the VTC displacement angle occurring immediately after the holding operation start is determined to be abnormal, and can improve accuracy and reliability in abnormality diagnosis.

The abnormality diagnosis process explained above is executed according to each routine in FIGS. 9 to 12 by the ECU 43. Hereinafter, the process content of each routine will be explained.

[Abnormality Diagnosis Routine]

An abnormality diagnosis routine in FIGS. 9 and 11 is executed at each calculating timing of an engine rotational speed during engine operating (for example, every 180° CA in a case of a four-cylinder engine). When the present routine is activated, first at step 1101, a target displacement angle vvttgt (target valve timing) in accordance with the present engine operating condition (engine rotational speed, intake pressure or the like) is calculated by a map or the like. After that, the process goes to step 1102, wherein an OCV current value (control duty dutyvvt) is feedback-controlled so that a deviation between the present VTC displacement angle vvt and the target displacement angle vvttgt is small.

Thereafter, the process goes to step 1103, wherein it is determined whether or not an abnormality diagnosis executing flag xvvtchk is set as “0” which means “not during abnormality diagnosis executing” (during dither control executing). When the abnormality diagnosis executing flag xvvtchk is set as “1”, it is determined that it is during abnormality diagnosis executing, and the process goes to the determination process at step 1105.

On the other hand, when it is determined at step 1103 that the abnormality diagnosis executing flag xvvtchk is set as “0”, it is determined that it is not during abnormality diagnosis executing (during dither control executing), and the process goes to step 1104, wherein it is determined whether or not an absolute value |vvttgt−vvt| of a deviation between the present target displacement angle vvttgt and the VTC displacement angle vvt is less than a first holding operation determination threshold value K1 (for example, one degree or less). As a result, when it is determined that the absolute value |vvttgt−vvt| of the deviation is greater than the first holding operation determination threshold value K1, it is determined that the holding operation execution condition is not met, and the process goes to step 1106, wherein a holding operation flag xvvtret is maintained to “0” and further, the present target displacement angle vvttgt is stored as the target displacement angle vvttgt 0 at holding operation start and also the abnormality diagnosis executing flag xvvtchk is reset as “0”, proceeding to step 1121 in FIG. 10.

On the other hand, when it is determined at step 1104 that the absolute value |vvttgt−vvt| of the deviation is less than the first holding operation determination threshold value K1, the process goes to step 1105, wherein it is determined whether or not a deviation |vvttgt−vvttgt 0| between the present target displacement angle vvttgt and the target displacement angle vvttgt 0 at holding operation start is less than a second holding operation determination threshold value K2 (for example, two degrees or less). As a result, when it is determined that the absolute value |vvttgt−vvttgt 0| of the deviation is less than the second holding operation determination threshold value K2, it is determined that the requirement of the target displacement angle change has occurred during holding operation executing and the process does not go to the holding operation execution steps subsequent to step 1107, but goes to step 1106, wherein the holding operation flag xvvtret is maintained to “0” and further, the present target displacement angle vvttgt is stored as the target displacement angle vvttgt 0 at holding operation start and also the abnormality diagnosis executing flag xvvtchk is reset as “0”, proceeding to step 1121 in FIG. 10.

When it is determined at step 1105 that a required value of the target displacement angle has changed even after entering into the holding operation, the holding operation and the abnormality diagnosis process are interrupted, and a usual target displacement angle F/B process may be executed.

In addition, when at step 1105, it is determined that the deviation |vvttgt−vvttgt 0| between the present target displacement angle vvttgt and the target displacement angle vvttgt 0 at holding operation start is less than the second holding operation determination threshold value K2, it is determined that the holding operation execution condition is met, and the process goes to step 1107, wherein the holding operation flag xvvtret is set as “1” which means “during holding operating”. After that, the process goes to step 1108, wherein holding operation start timing is determined based upon whether or not the previous value of the holding operation flag xvvtret is “0”.

As a result, when it is determined that it is not the holding operation timing, the process goes to step 1109 in FIG. 10 and when it is determined that it is the holding operation timing, the process goes to step 1109, wherein the holding operation time counter cvvtret is initialized to “0”. This holding operation time counter cvvtret is a time counter for counting an elapse time after the holding operation start by a timed relation process different from the present routine. In addition, at next step 1110, the present target displacement angle vvttgt is stored as the target displacement angle vvttgt 0 at holding operation start.

After that, at steps 1111 and 1112 in FIG. 10, it is determined whether or not a predetermined abnormality diagnosis execution condition (dither control execution condition) is met, as follows. First at step 1111, it is determined whether or not an elapse time after the holding operation start counted by the holding operation time counter cvvtret is more than a predetermined time K3 (for example, equal to 500 ms or more). This predetermined time K3 is set to time required from a point the holding operation start to a point the VTC displacement angle vvt corresponds to the target displacement angle and is stably held. When at step 1111, it is determined that the elapse time cvvtret after the holding operation start is less than the predetermined time K3, the abnormality diagnosis execution condition (dither control execution condition) is to be not met.

When at step 1111, it is determined that the elapse time cvvtret after the holding operation start is more than the predetermined time K3, whether or not the abnormality diagnosis execution precondition is met is determined based upon whether or not .the following conditions (1) to (3) are all satisfied.

-   -   (1) An engine rotational speed is more than a predetermined         rotational speed.     -   (2) An oil temperature of an engine is more than a predetermined         temperature.     -   (3) A discharge hydraulic pressure of the oil pump 27 is stable.

When at either one of steps 1111 and 1112, it is determined that the determination result is “NO” (i.e., in a case where an elapse time cvvtret after the holding operation start is less than the predetermined time K3 or, in a case where the abnormality diagnosis execution precondition is not met), it is determined that the abnormality diagnosis execution condition (dither control execution condition) is not met and the process goes to step 1116, wherein after a dither correction duty diz [%] of the hold duty is set as “0”, the process goes to step 1117. The present VTC displacement angle vvt is stored as a VTC displacement angle vvtret 0 at the time of no dither and at next step 1118, the abnormality diagnosis executing flag xvvtchk is reset as “0”, proceeding to step 1119.

On the other hand, when at both of steps 1111 and 1112, the determination result is “Yes” (i.e., in a case where an elapse time cvvtret after the holding operation start is more than the predetermined time K3 or, in a case where the abnormality diagnosis execution precondition is met), it is determined that the abnormality diagnosis execution condition (dither control execution condition) is met and the process goes to step 1113, wherein by referring to an increasing direction amplitude map in FIG. 13, an increasing direction amplitude dizp [%] of the hold duty is calculated in accordance with the present engine rotational speed ne and by referring to a decreasing direction amplitude map in FIG. 14, a decreasing direction amplitude dizm [%] of dither in the hold duty is calculated in accordance with the present engine rotational speed ne.

An amplitude map in each of both directions of the dither in FIGS. 13 and 14 is made in such a manner that as the engine rotational speed ne is higher (as the discharge hydraulic pressure of the oil pump 27 is higher), amplitudes dizp and dizm in both directions of the dither increase in stages. However, the present invention may be adapted such that amplitudes dizp and dizm in both directions of the dither are constant regardless of an engine rotational speed ne.

In addition, considering the characteristic that the hydraulic pressure in the advance hydraulic chamber 18 easier leaks than the hydraulic pressure in the retard hydraulic chamber 19 due to the structure of the vane-type variable valve timing controller 11, an increasing direction amplitude dizp (advance direction amplitude) of the dither of the hold duty is set to be slightly greater than a decreasing direction amplitude dizm thereof (retard direction amplitude). Thereby, a VTC displacement angle changing amount by the increasing direction amplitude dizp of the dither (advance direction amplitude) of the hold duty is designed to be substantially the same as the decreasing direction amplitude dizm thereof (retard direction amplitude). However, the present invention may be adapted such that the increasing direction amplitude dizp (advance direction amplitude) of the dither of the hold duty is equal to the decreasing direction amplitude dizm thereof (retard direction amplitude).

Thereafter, the process goes to step 1114, wherein the abnormality diagnosis executing flag xvvtchk is set as “1”. Thereafter, the process goes to step 1115, wherein a dither correction duty [%] to the hold duty drets is calculated by executing a dither correction duty calculation routine in FIG. 12 to be described later.

After that, the process goes to step 1119, wherein the hold duty drets (holding current) in advance learned is read out. In regard to the learning of the hold duty drets, if a certain hold duty learning condition is met for each execution of the holding operation, a learning value of the hold duty drets may be updated or a learning frequency of the hold duty drets is smaller for the each time. Further, the hold duty drets may be learned in each region of the target displacement angle vvttgt (or each engine operating condition) or a single hold duty drets which is common in all target displacement angles vvttgt (or all engine operating conditions) may be learned. The hold duty drers thus learned is stored in a writable, involatile memory such as a backup RAM of the ECU 43. In addition, at next step 1120 the dither correction duty diz is added to the hold duty drets to obtain a control duty dutyvvt. dutyvvt=drets+diz.

Thereafter, the process goes to step 1121, wherein the control duty dutyvvt is outputted to the hydraulic control valve 21. Thereby, the dither is applied to the control duty dutyvvt by the dither correction duty diz during the dither control period of the control duty dutyvvt.

After that, the process goes to step 1122, wherein it is determined whether or not the VTC displacement control is during holding operating based upon whether or not the holding operation flag xvvtret is set as “1”. When the valve timing control is not during holding operating, the present routine ends as it is.

On the other hand, when at step 1122 it is determined that the VTC displacement control is during holding operating (xvvtret=1), the process goes to step 1123, wherein it is determined whether or not the VTC displacement control is during abnormality diagnosis executing (dither control executing), based upon whether or not the abnormality diagnosis executing flag xvvtchk is set as “1”. When the VTC displacement control is not during abnormality diagnosis executing, the present routine ends as it is.

In addition, when at step 1123, wherein it is determined that the VTC displacement control is during abnormality diagnosis executing (xvvtchk=1), the process goes to step 1124, wherein it is determined whether or not an elapse time counted by the holding operation time counter cvvtret after the holding operation start is more than a predetermined time K4 (for example, 2000 ms or more). This predetermined time K4 is time required from the holding operation start to termination of the abnormality diagnosis (dither control). When at step 1124, it is determined that the elapse time cvvtret counted by the holding operation time counter after the holding operation start is less than the predetermined time K4, it is determined that the VTC displacement control is during abnormality diagnosis executing and the present routine ends as it is.

After that, at a point where the elapse time cvvtret counted by the holding operation time counter after the holding operation start reaches the predetermined time K4, at step 1124 the determination result is “Yes”, the process goes to step 1125, wherein a deviation between a VTC displacement angle vvtret 0 without the dither (immediately before the dither control start) and the present VTC displacement angle vvt (at the abnormality diagnosis termination) is calculated as an abnormality diagnosis deviation dvvtdg. dvvtdg=vvtret 0−vvt.

Thereafter, the process goes to step 1126, wherein it is determined whether or not an engine rotational speed is in a region of a low rotational side, based upon the present engine rotational speed is less than a predetermined value ne1 (for example, 1800 rpm or less). In this region the drain switching valves 34 and 35 are securely closed if the drain switching valve 34 and 35 are normal during holding operating. When the engine rotational speed is in this region of the low rotational side (engine rotational speed≦ne1), by steps 1128 to 1134, “open abnormality determination process” where presence/absence of open abnormality state in the drain switching valves 34 and 35 and/or the one-way valves 30 and 31 is determined is executed as follows

First, at step 1128 the abnormality diagnosis deviation dvvtdg is compared with a determination threshold value K5 (for example, +5° CA) of the open abnormality in the side of the advance hydraulic chamber 18. When it is determined that the abnormality diagnosis deviation dvvtdg is more than the determination threshold value K5 of the open abnormality in the side of the advance hydraulic chamber 18 (that is, a changing amount in the retard side of the VTC displacement angle during abnormality diagnosis period is more than the determination threshold value K5), it is determined that the open abnormality occurs in the drain switching valve 34 and/or the one-way valve 30 in the side of the advance hydraulic chamber 18, the process goes to step 1129, wherein the abnormality flag in the side of the advance hydraulic chamber xladvfail is set as “1” which means that there occurs the open abnormality. On the other hand, When it is determined that the abnormality diagnosis deviation dvvtdg is less than the determination threshold value K5 of the open abnormality in the side of the advance hydraulic chamber 18 (that is, a changing amount in the retard side of the VTC displacement angle during abnormality diagnosis period is less than the determination threshold value K5), it is determined that the open abnormality does not occur in the drain switching valve 34 and/or the one-way valve 30 in the side of the advance hydraulic chamber 18, and the process goes to step 1130, wherein the abnormality flag in the side of the advance hydraulic chamber xladvfail is set as “0” which means no occurrence of the open abnormality (normal).

Thereafter, the process goes to step 1131, wherein the abnormality diagnosis deviation dvvtdg is compared with a determination threshold value K6 (for example, −5° CA) of the open abnormality in the side of the retard hydraulic chamber 19. When it is determined that the abnormality diagnosis deviation dvvtdg is less than the determination threshold value K6 of the open abnormality in the side of the retard hydraulic chamber 19 (that is, a changing amount in the advance side of the VTC displacement angle during abnormality diagnosis period is more than an absolute value of the determination threshold value K6), it is determined that the open abnormality occurs in the drain switching valve 35 and/or the one-way valve 31 in the side of the retard hydraulic chamber 19, and the process goes to step 1132, wherein the abnormality flag in the side of the retard hydraulic chamber xlretfail is set as “1” which means that there occurs the open abnormality. On the other hand, When it is determined that the abnormality diagnosis deviation dvvtdg is more than the determination threshold value K6 of the open abnormality in the side of the retard hydraulic chamber 19 (that is, a changing amount in the advance side of the VTC displacement angle during abnormality diagnosis period is smaller than the absolute value of the determination threshold value K6), it is determined that the open abnormality does not occur in the drain switching valve 35 and/or the one-way valve 31 in the side of the retard hydraulic chamber 19, and the process goes to step 1133, wherein the abnormality flag in the side of the retard hydraulic chamber xlretfail is set as “0” which means no occurrence of the open abnormality (normal).

Thereafter, the process goes to step 1134, wherein an open abnormality determination process end flag xldiagend is set as “1” which means the open abnormality determination process end and the present routine ends. The open abnormality determination process end flag xldiagend is cleared to “0” by an initialization process at power supply to the ECU 43 and thereafter, is used for determining whether or not the aforementioned open abnormality determination process is executed during the subsequent engine operating.

On the other hand, when it is determined at step 1126 that the present engine rotational speed is not in a region of the low rotational side (engine rotational speed≦ne1), the process goes to step 1127, wherein it is determined whether or not the engine rotational speed is in a region of a high rotational side where the drain switching valves 34 and 35 are forcibly opened by a rotational centrifugal force during holding operating if they are normal to create the state where the one-way valves 30 and 31 at both the sides do not function, based upon whether or not the present rotational speed is more than a predetermined value ne2 (for example, 1800 rpm or more). When the present engine rotational speed is not in a region of the high rotational side, either, that is, when the present engine rotational speed is in an intermediate region between the determination threshold value ne1 in a region of the low rotational side and the determination threshold value ne2 in a region of the high rotational side, since it is not clear whether or not the drain switching valves 34 and 35 are forcibly opened by the rotational centrifugal force, the abnormality diagnosis process is not executed at all and the present routine ends as it is.

In contrast, when at step 1127, the present rotational speed is more than the predetermined value ne2, it is determined that the engine rotational speed is in a region of the high rotational side where the drain switching valves 34 and 35 are forcibly opened by a rotational centrifugal force during holding operating if they are normal to create the state where the one-way valves 30 and 31 at both the sides do not function. In consequence, by steps 1135 to 1141, “closed abnormality determination process” where presence/absence of the closed abnormality state in the drain switching valves 34 and 35 is determined is executed as follows.

First, at step 1128 the abnormality diagnosis deviation dvvtdg is compared with a determination threshold value K7 (for example, +5° CA) of the closed abnormality in the side of the retard hydraulic chamber 19. When it is determined that the abnormality diagnosis deviation dvvtdg is more than the determination threshold value K7 of the closed abnormality in the side of the retard hydraulic chamber 19 (that is, a changing amount in the retard side of the VTC displacement angle during abnormality diagnosis period is more than the determination threshold value K7), it is determined that the closed abnormality occurs in the drain switching valve 35 in the side of the retard hydraulic chamber 19, and the process goes to step 1136, wherein the closed abnormality flag in the side of the retard hydraulic chamber x2retfail is set as “1” which means that there occurs the closed abnormality. On the other hand, When it is determined that the abnormality diagnosis deviation dvvtdg is less than the determination threshold value K7 of the closed abnormality in the side of the retard hydraulic chamber 19 (that is, a changing amount in the retard side of the VTC displacement angle during abnormality diagnosis period is less than the determination threshold value K7), it is determined that the closed abnormality does not occur in the drain switching valve 35 in the side of the retard hydraulic chamber 19, and the process goes to step 1137, wherein the closed abnormality flag in the side of the retard hydraulic chamber x2retfail is set as “0” which means no occurrence of the closed abnormality (normal).

Thereafter, the process goes to step 1138, wherein the abnormality diagnosis deviation dvvtdg is compared with a determination threshold value K8 (for example, −5° CA) of the closed abnormality in the side of the advance hydraulic chamber 18. When it is determined that the abnormality diagnosis deviation dvvtdg is less than the determination threshold value K8 of the closed abnormality in the side of the advance hydraulic chamber 18 (that is, a changing amount in the advance side of the VTC displacement angle during abnormality diagnosis period is more than an absolute value of the determination threshold value K8), it is determined that the closed abnormality occurs in the drain switching valve 34 in the side of the advance hydraulic chamber 18, and the process goes to step 1139, wherein the closed abnormality flag in the side of the advance hydraulic chamber x2advfail is set as “1” which means that there occurs the closed abnormality. On the other hand, When it is determined that the abnormality diagnosis deviation dvvtdg is more than the determination threshold value K8 of the closed abnormality in the side of the advance hydraulic chamber 18 (that is, a changing amount in the advance side of the VTC displacement angle during abnormality diagnosis period is smaller than the absolute value of the determination threshold value K8), it is determined that the closed abnormality does not occur in the drain switching valve 34 in the side of the advance hydraulic chamber 18, and the process goes to step 1140, wherein the closed abnormality flag in the side of the advance hydraulic chamber x2advfail is set as “0” which means no occurrence of the closed abnormality (normal).

Thereafter, the process goes to step 1141, wherein a closed abnormality determination process end flag x2ldiagend is set as “1” which means the closed abnormality determination process end and the present routine ends. The closed abnormality determination process end flag x2diagend is cleared to “0” by an initialization process at power supply to the ECU 43 and thereafter, is used for determining whether or not the aforementioned closed abnormality determination process is executed during the subsequent engine operating.

[Dither Correction Duty Calculation Routine]

A dither correction duty calculation routine in FIG. 12 is a subroutine executed at step 1115 in FIG. 10. However, the present routine is executed for each predetermined time (for example, each of 2 ms).

When the present routine is activated, first at step 1201 it is determined whether or not the previous diz is “0”, that is, this process is a cycle for executing calculation of diz for the first time. When at step 1201 it is determined that the previous diz is “0”, the process goes to step 1202, wherein an amplitude direction switching counter cdiz for counting an elapse time after having switched an amplitude direction of a dither is initialized to “0”. At next step 1203, an increasing direction amplitude dizp (advance direction amplitude) calculated at step 1113 in FIG. 10 is set as a dither correction duty and further, an amplitude direction determination flag xdiz is set as “0” which means the increasing direction amplitude, proceeding to step 1204.

On the other hand, when at step 1201 it is determined that the previous diz is not “0”, the steps 1202 and 1203 are skipped and the process goes to step 1204. At step 1204, the amplitude direction switching counter cdiz is made by counting up the previous value cdiz [I−1] by “1”. cdiz=cdiz[I−1]+1.

After that, the process goes to step 1205, wherein by referring to an amplitude direction switching time map in FIG. 15, an amplitude direction switching time tmdiz is calculated in accordance with the present engine rotational speed ne. This amplitude direction switching time tmdiz is time required for switching the amplitude direction and corresponds to ½ of the dither cycle. The amplitude direction switching time map in FIG. 15 is set in a manner that, considering that as an engine rotational speed ne is higher, a discharge hydraulic pressure of the oil pump 27 is higher, as the engine rotational speed ne is higher, the amplitude direction switching time tmdiz is shorter by stages. However, the present invention may set the amplitude direction switching time tmdiz to be constant regardless of an engine rotational speed ne.

In addition, in the amplitude direction switching time map in FIG. 15, an amplitude direction switching time tmdiz (dither cycle/2) in each of the present engine rotational speed ne is set close to the minimum time in which the hydraulic pressure can be transmitted to each hydraulic chamber 18 and 19 in the increasing direction amplitude and the decreasing direction amplitude of the holding current in consideration of a delay of a hydraulic transmission system to the hydraulic chambers 18 and 19 respectively. In this way, the VTC displacement angle changing amount at a normal operation state is reduced and at the same time, the VTC displacement angle changing amount at an abnormal operation state is increased. In consequence, a difference in VTC displacement angle changing amount between at a normal operation state and at an abnormal operation state is clarified, making it possible to easily detect the abnormality.

Thereafter, the process goes to step 1206, wherein it is determined whether or not the time counted in the amplitude direction switching counter cdiz reaches more than the amplitude direction switching time tmdiz calculated at step 1205. When the time counted in the amplitude direction switching counter cdiz does not reach the amplitude direction switching time tmdiz yet, the present routine ends as it is.

After that, at a point when the time counted in the amplitude direction switching counter cdiz has reached the amplitude direction switching time tmdiz calculated at step 1205, the process goes to step 1207, wherein it is determined whether or not the amplitude direction determination flag xdiz is set as “1” which means the decreasing direction amplitude. Since at the dither starting, at step 1203 the amplitude direction determination flag xdiz is set as “0” which means the increasing direction amplitude, it is determined at step 1207 that the determination result is “No”. Therefore, the process goes to step 1209, wherein a decreasing direction amplitude dizm (retard direction amplitude) calculated at step 1113 in FIG. 10 is set as a dither correction duty diz and further, and an amplitude direction determination flag xdiz is set as “1” which means the decreasing direction amplitude. At next step 1210, 04 the amplitude direction switching counter cdiz is initialized to “0” and the present routine ends. Thereby, the amplitude direction of the dither is reversed from increasing direction to decreasing direction.

After that, at a point when the time counted in the amplitude direction switching counter cdiz has reached the amplitude direction switching time tmdiz calculated at step 1205, at step 1207 the determination result is “Yes”, and the process goes to step 1208, wherein an increasing direction amplitude dizp (advance direction amplitude) calculated at step 1113 in FIG. 10 is set as a dither correction duty diz and further, an amplitude direction determination flag xdiz is set as “0” which means the increasing direction amplitude. At next step 1210, the amplitude direction switching counter cdiz is initialized to “0” and the present routine ends. Thereby, the amplitude direction of the dither is reversed from decreasing direction to increasing direction.

By repetition of the aforementioned processes, the amplitude direction of the dither is reversed each time the time counted in the amplitude direction switching counter cdiz reaches the amplitude direction switching time tmdiz.

One example of the abnormality diagnosis in the present embodiment described above is shown in a time chart of FIG. 8. In the example of FIG. 8, at time t1 a target displacement angle vvttgt changes in the advance direction and according to it, a VTC displacement angle vvt is feedback-controlled in such a manner as to change in the advance direction. In consequence, at time t2 when an absolute value of a deviation between the target displacement angle vvttgt and the VTC displacement angle vvt is less than a predetermined value and a predetermined holding operation execution condition is met, the holding operation starts. The period from this holding operation start until the elapse of the predetermined time K3 is determined to be a period required for the VTC displacement angle vvt to correspond to the target displacement angle vvttgt for stable holding, and the control duty dutyvvt is set only to a learning value of the hold duty drets and the dither is not applied to the control duty dutyvvt.

Thereafter, at time t3 when the predetermined time K3 has elapsed from the holding operation start, the abnormality diagnosis condition (dither control execution condition) is met to start the dither control. During this dither controlling, the increasing direction amplitude dizp (advance direction amplitude) and the decreasing direction amplitude dizm (retard direction amplitude) are alternately added to the hold duty (learning value) of the hydraulic control valve 21 for each amplitude direction switching time tmdiz. Thereby, the control duty of the hydraulic control valve 21 is alternately switched in the amplitude direction of the dither centered at the hold duty drets for each amplitude direction switching time tmdiz to perform the dither control of the amplitudes dizp and dizm.

In an example in FIG. 8, a chain line shows a behavior of a VTC displacement angle vvt when the open abnormality state occurs where the drain switching valve 34 and/or the one-way valve 30 in the side of the advance hydraulic chamber 18 remain to be opened.

In a case of performing the holding operation at a region of the low rotation side, when both of the drain switching valves 34 and 35 at the side of the advance hydraulic chamber 18 and at the side of the retard hydraulic chamber 19 operate normally, both of the drain switching valves 34 and 35 close. Therefore, when both of the one-way valves 30 and 31 are normal, the reverse flow prevention function of both of the one-way valves 30 and 31 can be effectively achieved. Therefore, even when the dither is applied to the hold duty drets, the VTC displacement angle vvt is held close to the target displacement angle vvttgt. However, when the drain switching valve 34 and/or the one-way valve 30 at the side of the advance hydraulic chamber 18 is in an open abnormality state, the hydraulic pressure in the advance hydraulic chamber 18 where the open abnormality state is occurring is leaked through the drain switching valve 34 or the one-way valve 30 and is reduced. Therefore, the hydraulic pressure in the retard hydraulic chamber 19 is greater than the hydraulic pressure in the advance hydraulic chamber 18, creating the phenomenon that the VTC displacement angle displaces in the retard direction.

At time t4 when the dither control is executed for a predetermined time (at time t4 when a predetermined time K4 elapses from the holding operation start), the dither control is terminated to return the control duty dutyvvt of the hydraulic control valve 21 to the hold duty drets only, and further, a deviation between a VTC displacement angle vvtret 0 without dither (immediately before the dither control start) and a VTC displacement angle vvt at time t4 of dither control termination (at abnormality diagnosis termination) is calculated as an abnormality diagnosis deviation dvvtdg. In addition, the abnormality diagnosis deviation dvvtdg is compared with a determination threshold value K5 (for example, +5° CA) of the open abnormality in the side of the advance hydraulic chamber 18. Based upon whether or not the abnormality diagnosis deviation dvvtdg is more than the determination threshold value K5 of the open abnormality in the side of the advance hydraulic chamber 18 (a changing amount in the retard side of the VTC displacement angle during abnormality diagnosis period is more than the determination threshold value K5), it is determined whether or not the open abnormality occurs in the drain switching valve 34 and/or the one-way valve 30 in the side of the advance hydraulic chamber 18.

In a behavior of the VTC displacement angle shown in one chain line of FIG. 8, when the abnormality diagnosis deviation dvvtdg is more than the determination threshold value K5 as the open abnormality in the side of the advance hydraulic chamber 18, the open abnormality in the side of the advance hydraulic chamber 18 is determined, setting the open abnormality flag xladvfail in the side of the advance hydraulic chamber to “1” which means that there occurs the open abnormality.

According to the present embodiment described above, since the control duty in the hydraulic control chamber 21 dutyvvt is vibrated during hold operating, the determination can be made as to presence/absence of abnormality in the drain switching valves 34 and 35 and/or the one-way valves 30 and 31, based upon whether or not the changing degree of the VTC displacement angle vvt due to vibration of the control duty dutyvvt is great. As a result, the abnormality in the drain switching valves 34 and 35 or the one-way valves 30 and 31 can be quickly detected.

It should be noted that according to the abnormality diagnosis system of the present embodiment, when both the drain switching valves 34 and 35 (or one-way valves 30 and 31) in the side of the advance hydraulic chamber 18 and the side of the retard hydraulic chamber 19 are simultaneously in an open abnormality state, it may be hard to detect the abnormality, but probability that both the drain switching valves 34 and 35 (or one-way valves 30 and 31) are simultaneously abnormal is extremely small as compared to the probability that either one of the drain switching valves (or one-way valves) is abnormal, and therefore, the abnormality in most cases can be quickly detected by the abnormality diagnosis method of the present embodiment.

In addition in the present invention, a hydraulic switching valve for switching the hydraulic pressure driving the drain switching valves 34 and 35 may be separated from the hydraulic control valve 21, but the present embodiment is so structured that the hydraulic switching valve is integral with the hydraulic control valve 21, and therefore, has an advantage of being capable of meeting the requirements such as reduction in the number of component parts, reduction in costs and downsizing.

Further, the present embodiment detects the abnormality by using the following method, considering that in a region of a high-rotation side where an engine rotational speed is more than a predetermined value, the drain switching valves 34 and 35 respectively are forcibly opened due to the rotational centrifugal force all the time regardless of the control hydraulic pressure in the drain switching valves 34 and 35 respectively, creating the state where the functions of the respective one-way valves 30 and 31 do not work. That is, in a case of performing the holding operation in a region of a low rotational side, the control duty in the hydraulic control chamber 21 dutyvvt is vibrated to determine presence/absence of the open abnormality states in the drain switching valves 34 and 35 and/or the one-way valves 30 and 31 and also in a case of performing the holding operation in a region of a high rotational side, the control duty in the hydraulic control chamber 21 dutyvvt is vibrated to determine presence/absence of the closed abnormality states in the drain switching valves 34 and 35. As a result, both of “open abnormality” and “closed abnormality” can be quickly detected.

However, the present invention may be structured such that in a region of a high rotational side, respective drain switching valves 34 and 35 are not opened by a rotational centrifugal force.

Embodiment 3

In Embodiment 3, the open abnormality will be detected as follows.

When both of the drain switching valves 34 and 35 in the side of the advance hydraulic chamber 18 and in the side of the retard hydraulic chamber 19 operate normally during holding operating, both of the drain switching valves 34 and 35 close. Therefore, when both of the one-way valves 30 and 31 are normal, a reverse flow prevention function of each of the one-way valves 30 and 31 can be made to effectively operate. However, when there occurs the open abnormality state where either one of the drain switching valves 34 and 35 (or the one-way valves 30 and 31) remains to be opened, either one of the drain switching valves 34 and 35 (or the one-way valves 30 and 31) is fixed in a state of being opened even during the holding operating. Accordingly, when either one of the drain switching valves 34 and 35 (or the one-way valves 30 and 31) is in an open abnormality state, the hydraulic pressures in the hydraulic chambers 18 and 19 in the side where the open abnormality occurs are leaked through the drain switching valves 34 and 35 (or the one-way valves 30 and 31) and reduced. In consequence, the balance in hydraulic pressure between the hydraulic chambers 18 and 19 is off, being unable of maintaining the VTC displacement angle at a constant position, so that there occurs the phenomenon where a changing amount of the VTC displacement angle increases.

Considering this characteristic, Embodiment 3 is adapted to determine whether or not the drain switching valves 34 and 35 and/or the one-way valves 30 and 31 are in an open abnormality state based upon whether or not a changing amount of the VTC displacement angle within a predetermined period exceeds a normal range during holding operating.

In this case, there are considered various methods of detecting a changing amount of the VTC displacement angle within a predetermined period during holding operating. For example, the following methods are considered.

[Method (1) of Detecting a Changing Amount of the VTC Displacement Angle During Holding Operating]

A difference between a VTC displacement angle immediately after start of the holding operation and a VTC displacement angle at elapse of a predetermined period is calculated and the determination is made as to presence/absence of open abnormality states of the drain switching valves 34 and 35 and/or the one-way valves 30 and 31 based upon this difference. In this way, a case where the VTC displacement angle at the elapse of a predetermined period displaces largely in the retard direction relative to the VTC displacement angle immediately after the start of the holding operation and a case where it displaces excessively in the advance direction are distinguished and determined, so that it can be determined which side of the advance hydraulic chamber 18 and the retard hydraulic chamber 19 the open abnormality states of the drain switching valves 34 and 35 (or the one-way valves 30 and 31) have occurred in, being capable of identifying the occurrence location of the open abnormality state.

For example, as shown in a chain line of FIG. 16, when the VTC displacement angle during holding operating displaces excessively in the retard direction, it can be determined that the drain switching valve 34 (or the one-way valve 30) in the side of the advance hydraulic chamber 18 for effecting the hydraulic pressure in the advance direction relative to the vane 17 is in an open abnormality state and the hydraulic pressure in the advance hydraulic chamber 18 is leaked through the drain switching valve 34 (or the one-way valve 30) and reduced. In addition, when the VTC displacement angle during holding operating displaces excessively in the advance direction, it can be determined that the drain switching valve 35 (or the one-way valve 31) in the side of the retard hydraulic chamber 19 for effecting the hydraulic pressure in the retard direction relative to the vane 17 is in an open abnormality state and the hydraulic pressure in the retard hydraulic chamber 19 is leaked through the drain switching valve 35 (or the one-way valve 31) and reduced.

[Method (2) of Detecting a Changing Amount of the VTC Displacement Angle During Holding Operating]

In a case where both of the drain switching valves 34 and 35 in the side of the advance hydraulic chamber 18 and in the side of the retard hydraulic chamber 19 are in an open abnormality, since during holding operating (particularly during holding operating in a low rotational region where the supply hydraulic pressure from the oil pump 27 is low), return of the VTC displacement angle due to friction torque of the cam shaft occurs in a timed relation to rotation of the cam shaft, there occurs the phenomenon that the VTC displacement angle vibrates relatively largely cantered at a target displacement angle alternately in the advance direction and in the retard direction in a timed relation to rotation of the cam shaft as shown in FIG. 17.

Considering this characteristic, Embodiment 3 detects the maximum value and the minimum value of the VTC displacement angle from a point immediately after start of the holding operation to a point at elapse of a predetermined period and calculates a difference therebetween, determining presence/absence of open abnormality states of the drain switching valves 34 and 35 and/or the one-way valves 30 and 31 based upon this difference. In this case, the maximum margin in the vibration range of the VTC displacement angle is found from the difference between the maximum value and the minimum value of the VTC displacement angle. Accordingly when the difference between the maximum value and the minimum value of the VTC displacement angle (the maximum margin of the vibration range) exceeds a normal range, it can be determined that the drain switching valve 34 and 35 and/or the one-way valves 30 and 31 in the side of the advance hydraulic chamber 18 and the side of the retard hydraulic chamber 19 are in an open abnormality state.

[Method (3) of Detecting a Changing Amount of the VTC Displacement Angle Period During Holding Operating]

Embodiment 3 detects the maximum value and the minimum value of the VTC displacement angle from a point immediately after start of the holding operation to a point at elapse of a predetermined period and calculates a deviation between a target displacement angle during holding operating and the maximum value and a deviation between the target displacement angle and the minimum value, determining presence/absence of open abnormality states of the drain switching valves 34 and 35 and/or the one-way valves 30 and 31 based upon these two deviations. In consequence, when a changing amount (deviation) in the advance direction of the VTC displacement angle and a changing amount (deviation) in the retard direction of the VTC displacement angle are compared by using a target displacement angle as reference and the changing amounts (deviations) in both directions are substantially equal, it can be determined that the drain switching valve 34 and 35 and/or the one-way valves 30 and 31 in the side of the advance hydraulic chamber 18 and the side of the retard hydraulic chamber 19 are in an open abnormality state. On the other hand, in a case where the changing amount (deviation) in the one side only is excessively large, it can be determined that the drain switching valve 34 and 35 (or the one-way valves 30 and 31) in the one side only are in an open abnormality state. Accordingly, the open abnormality states in both of the side of the advance hydraulic chamber 18 and the side of the retard hydraulic chamber 19 and the open abnormality state in the one side only can be distinguished and determined.

In the following description, for convenient explanation, a combination of “one-way valve” and “drain switching valve” is described in “one-way valve mechanism” and “open abnormality (state) of one-way valve and/or drain switching valve” is described in “open abnormality (state) of one-way valve mechanism”.

Embodiment 3 executes an abnormality diagnosis routine of each in FIGS. 18 to 20 by the ECU 43 and determines a changing amount of the VTC displacement angle within a predetermined period during holding operating by combining three methods (1) to (3) of detecting a changing amount of the VTC displacement angle, determining presence/absence of open abnormality states in the drain switching valves 34 and 35 and/or the one-way valves 30 and 31 as follows.

An abnormality diagnosis routine in FIGS. 18 and 20 is executed at each calculating timing of an engine rotational speed during engine operating (for example, every 180° CA in a case of a four-cylinder engine). When the present routine is activated, first at step 2101 a target displacement angle vvttgt (target valve timing) in accordance with the present engine operating condition (engine rotational speed, intake pressure or the like) is calculated by a map or the like. After that, the process goes to step 2102, wherein an OCV current value (control duty dutyvvt) is feedback-controlled so that a deviation between the present VTC displacement angle vvt and the target displacement angle vvttgt becomes small.

Thereafter, the process goes to step 2103, wherein it is determined whether or not an abnormality diagnosis executing flag xvvtchk is cleared to “0” which means “not during abnormality diagnosis executing”. When the abnormality diagnosis executing flag xvvtchk is set as “1”, it is determined that it is during abnormality diagnosis executing, the process goes to the determination process at step 2105.

On the other hand, when it is determined at step 2103 that the abnormality diagnosis executing flag xvvtchk is cleared to “0”, it is determined that it is not during abnormality diagnosis executing, and the process goes to step 2104, wherein it is determined whether or not an absolute value |vvttgt−vvt| of a deviation between the present target displacement angle vvttgt and the VTC displacement angle vvt is less than a holding operation determination threshold value K1 (for example, one degree or less). As a result, when it is determined that the absolute value |vvttgt−vvt| of the deviation is greater than the holding operation determination threshold value K1, it is determined that the holding operation execution condition is not met, and the process goes to step 2106, wherein the abnormality operation executing flag xvvtchk is cleared to “0”, proceeding to step 2117 in FIG. 19.

On the other hand, when it is determined at step 2104 that the absolute value |vvttgt−vvt| of the deviation is less than the holding operation determination threshold value K1, the process goes to step 2105, wherein whether or not the abnormality diagnosis execution condition is met is determined based upon whether or not .the following conditions (1) to (3) are all satisfied, for example.

-   -   (1) An engine rotational speed is more than a predetermined         rotational speed.     -   (2) An oil temperature of an engine (cooling water temperature)         is more than a predetermined temperature.     -   (3) A discharge hydraulic pressure of the oil pump 27 is more         than a predetermined value.

When any one of these three conditions (1) to (3) is not satisfied, it results in that the abnormality diagnosis execution condition is not met and the process goes to step 2106, wherein the abnormality operation executing flag xvvtchk is cleared to “0”, proceeding to step 2117 in FIG. 19.

On the other hand, when these three conditions (1) to (3) are all satisfied, it is determined that the abnormality diagnosis execution condition is met and the process goes to step 2107, wherein the pre-learned hold duty (holding current) is read out to start the holding operation and at the same time, start the abnormality diagnosis process.

It should be noted that, as for the learning of the hold duty, when a predetermined hold duty learning condition is met, a learning value of the hold duty may be updated for each time or the learning frequency of the hold duty may be smaller than this. Further, the hold duty may be learned at each region of the target displacement angle vvttgt (or each engine operating region) and a single hold duty which is in common among all target displacement angles (or all engine operating regions) may be learned. Such learned hold duty is updated and stored in a rewritable, involatile memory such as a backup RAM in the ECU 43.

And it is determined at step 2108 whether or not the abnormality diagnosis executing flag xvvtchk is set as “0”. When the abnormality diagnosis executing flag xvvtchk is set as “1,”, it is determined that it is during abnormality diagnosis executing, and the process skips initialization processes at start of the abnormality diagnosis at steps 2109 to 2112 and goes to the determination process step 2113 in FIG. 19.

On the other hand, in a case where it is determined at step 2105 that the abnormality diagnosis execution condition is met and also it is determined at step 2108 that the abnormality diagnosis executing flag xvvtchk is “0”, it is determined that the VTC displacement control is at start of the abnormality diagnosis and the initialization processes at start of the abnormality diagnosis at steps 2109 to 2112 are executed.

At the initialization process at start of the abnormality diagnosis, at step 2109 an abnormality diagnosis execution time counter cvvtret is initialized to “0”. This abnormality diagnosis execution time counter cvvtret is a time counter for counting an elapse time after starting the abnormality diagnosis (after starting the holding operation) by a time-related process different from the present routine. In addition, at next step 2110 the present VTC displacement angle vvt is stored as a VTC displacement angle vvtret 0 at start of the abnormality diagnosis (start of the holding operation). Thereafter, the process goes to step 2111, wherein the present VTC displacement angle wt is stored as each of an initial value of the minimum value of the VTC displacement angle vvtmin and an initial value of the maximum value of the VTC displacement angle vvtmax. After that, the process goes to step 2112, wherein the abnormality diagnosis executing flag xvvtchk is set as “1” which means “during abnormality diagnosis executing” and the process goes to the determination process at step 2113 in FIG. 19.

In addition, at step 2113 in FIG. 19 the stored value of the minimum value of the VTC displacement angle vvtmin and the present VTC displacement angle vvt are compared. When the present VTC displacement angle vvt is smaller than the stored value of the minimum value of the VTC displacement angle vvtmin, the process goes to step 2114, wherein the present VTC displacement angle vvt is updated and stored as the minimum value of the VTC displacement angle vvtmin. However, when the present VTC displacement angle vvt is greater than the stored value of the minimum value of the VTC displacement angle vvtmin, the stored value of the minimum value of the VTC displacement angle vvtmin is not updated. During the abnormality diagnosis period, the processes at steps 2113 and 2114 are repeated, thereby updating and storing the minimum value of the VTC displacement angle vvtmin during the abnormality diagnosis period.

Thereafter, the process goes to step 2115, wherein the stored value of the maximum value of the VTC displacement angle vvtmax and the present VTC displacement angle vvt are compared. When the present VTC displacement angle vvt is greater than the stored value of the maximum value of the VTC displacement angle vvtmax, the process goes to step 2116, wherein the present VTC displacement angle vvt is updated and stored as the maximum value of the VTC displacement angle vvtmax. However, when the present VTC displacement angle vvt is smaller than the stored value of the maximum value of the VTC displacement angle vvtmax, the stored value of the maximum value of the VTC displacement angle vvtmax is not updated. During the abnormality diagnosis period, the processes at steps 2115 and 2116 are repeated, thereby updating and storing the maximum value of the VTC displacement angle vvtmax during the abnormality diagnosis period.

And it is determined at next step 2117 whether or not the abnormality diagnosis executing flag xvvtchk is set as “1”. When the abnormality diagnosis executing flag xvvtchk is not set as “1”, it is determined that it is not during abnormality diagnosis executing, and the present routine ends as it is.

On the other hand, when it is determined at next step 2117 that the abnormality diagnosis executing flag xvvtchk is set as “1”, it is determined that it is during abnormality diagnosis executing and the process goes to step 2118, wherein it is determined whether or not the abnormality diagnosis execution time (elapse time from start of the abnormality diagnosis) measured by the abnormality diagnosis execution time counter cvvtret is more than a predetermined time K2 (for example, 3000 ms or more). When it does not reach the predetermined time K2, the present routine ends as it is.

Thereafter, at a point when the measured time by the abnormality diagnosis execution time counter cvvtret has reached the predetermined time K2, the determination result at step 2118 is “Yes”, and the process goes to step 2119. A deviation between the VTC displacement angle at start of the abnormality diagnosis vvtret 0 and the VTC displacement angle at the present time (at termination of the abnormality diagnosis) is calculated and this deviation is stored as a first abnormality diagnosis deviation dvvtdg1. dvvtdg1=vvtret 0−vvt.

The first abnormality diagnosis deviation dvvtdg1 is an abnormality diagnosis parameter representing how much the VTC displacement angle vvt at termination of the abnormality diagnosis has changed in the advance or retard direction relative to the VTC displacement angle vvtret o at start of the abnormality diagnosis. When the deviation is a plus value, it represents that the VTC displacement angle vvt at termination of the abnormality diagnosis has changed in the retard direction and when the deviation is a minus value, it represents that the VTC displacement angle vvt at termination of the abnormality diagnosis has changed in the advance direction.

Thereafter, the process goes to step 2120, wherein a deviation between the maximum value of the VTC displacement angle vvtmax and the minimum value of the VTC displacement angle vvtmin is calculated and this deviation is stored as a second abnormality diagnosis deviation dvvtdg2. dvvtdg2=vvtmax−vvtmin.

The second abnormality diagnosis deviation dvvtdg2 is an abnormality diagnosis parameter representing the maximum margin of the vibration range of the VTC displacement angle vvt during abnormality diagnosing.

Thereafter, at next step 2121, a deviation between the maximum value of the VTC displacement angle vvtmax during abnormality diagnosing and the present (during abnormality diagnosing) target displacement angle vvttgt is calculated (vvtmax−vvttgt) and also a deviation between the minimum value of the VTC displacement angle vvtmin and the present (during abnormality diagnosing) target displacement angle vvttgt is calculated (vvtmin−vvttgt). An absolute value by addition of these two deviations is stored as a third abnormality diagnosis deviation dvvtdg3. dvvtdg3=|(vvtmax−vvttgt)+(vvtmin−vvttgt)|.

The third abnormality diagnosis deviation dvvtdg3 is an abnormality diagnosis parameter representing how much the vibration range of the VTC displacement angle vvt during abnormality diagnosing deviates in the advance direction or in the retard direction from the vibration range centered at the target displacement angle vvttgt. As shown in FIG. 3, in a case where the center of the vibration range of the VTC displacement angle vvt during abnormality diagnosing is close to the target displacement angle vvttgt, one deviation (vvtmax−vvttgt) becomes a plus value and the other deviation (vvtmin−vvttgt) becomes a minus value and also since an absolute vale of the one deviation is close to an absolute value of the other deviation, the third abnormality diagnosis deviation dvvtdg3 is close to “0”. That is, as the third abnormality diagnosis deviation dvvtdg3 becomes greater, the vibration range of the VTC displacement angle vvt during abnormality diagnosing deviates largely in the advance direction or in the retard direction. The third abnormality diagnosis deviation dvvtdg3 and the second abnormality diagnosis deviation dvvtdg2 are used for distinguishing and determining the open abnormality of the one-way valve mechanisms in both of the side of the advance hydraulic chamber 18 and the side of the retard hydraulic chamber 19 and the open abnormality of the one-way valve mechanism in one side only of the advance hydraulic chamber 18 and the retard hydraulic chamber 19.

Thereafter, the process goes to step 2122 in FIG. 20, wherein it is determined whether or not the third abnormality diagnosis deviation dvvtdg3 is smaller than a predetermined value K3 (for example, one degree). When it is determined that the third abnormality diagnosis deviation dvvtdg3 is more than the predetermined value K3, since the vibration range of the VTC displacement angle vvt during abnormality diagnosing displaces largely in the advance direction or in the retard direction, it is determined that there does not occur the state where the one-way valve mechanisms in both of the side of the advance hydraulic chamber 18 and the side of the retard hydraulic chamber 19 are in an open abnormality state and the process goes to step 2124. The open abnormality flag for both one-way valve mechanisms xwopenfail is cleared to “0”.

In contrast, when it is determined at step 2122 that the third abnormality diagnosis deviation dvvtdg3 is smaller than the predetermined value K3, the process goes to step 2123, wherein it is determined whether or not the second abnormality diagnosis deviation dvvtdg2 is smaller than a predetermined value K4 (for example, 7 degrees). As a result, when it is determined that the second abnormality diagnosis deviation dvvtdg2 is more than the predetermined value K4, since the maximum margin in the vibration range of the VTC displacement angle vvt during abnormality diagnosing exceeds a normal range, it is determined that there occurs the state where the one-way valve mechanisms in both of the side of the advance hydraulic chamber 18 and the side of the retard hydraulic chamber 19 are in an open abnormality state and the process goes to step 2125. The open abnormality flag for both the one-way valve mechanisms xwopenfail is set as “1” and thereafter, the process goes to step 2132, wherein an abnormality diagnosis process end flag xdiagend is set as “1,” which means an abnormality diagnosis process termination. Then the present routine ends. The abnormality diagnosis process end flag xdiagend is cleared to “0” by the initialization process at power supply to the ECU 43 and is used to determine whether or not the aforementioned open abnormality determination process is executed during subsequent engine operating.

On the other hand, when it is determined at step 2122 that the third abnormality diagnosis deviation dvvtdg3 is smaller than the predetermined value K3 and also when at step 2123 it is determined that the second abnormality diagnosis deviation dvvtdg2 is smaller than the predetermined value K4, it is determined that there does not occur the state where the one-way valve mechanisms in both the sides are not in an open abnormality state and the process goes to step 2124. The open abnormality flag for both one-way valve mechanisms xwopenfail is cleared to “0”.

In other words, only when the third abnormality diagnosis deviation dvvtdg3 is smaller than the predetermined value K3 and also when the second abnormality diagnosis deviation dwwtdg2 is greater than the predetermined value K4 (that is, a case where the VTC displacement angle vibrates centered at close to a target displacement angle vvttgt and the maximum margin of the vibration range exceeds a normal range), it is determined that there occurs the state where the one-way valve mechanisms in both the sides are in an open abnormality state and the process goes to step 2125. The open abnormality flag for both the one-way valve mechanisms xwopenfail is set as “1”. Other than that, the open abnormality flag for both the one-way valve mechanisms xwopenfail is cleared to “0”.

Thereafter, the process goes to step 2126, wherein it is determined whether or not the first abnormality diagnosis deviation dvvtdg1 is more than a predetermined value K5 (for example, 5 deg or more). When the first abnormality diagnosis deviation dvvtdg1 is more than the predetermined value K5, since the VTC displacement angle vvt at a termination of the abnormality diagnosis changes excessively largely in the advance direction relative to the VTC displacement angle vvtret 0 at start of the abnormality diagnosis, it is determined that the one-way valve mechanism in the side of the advance hydraulic chamber 18 is in an open abnormality state and the process goes to step 2127. The open abnormality flag for the one-way valve mechanism in the side of the advance hydraulic chamber xadvfail is set as “1”. On the other hand, when the first abnormality diagnosis deviation dvvtdg1 is less than the predetermined value K5, the process goes to step 2128. The open abnormality flag for the one-way valve mechanism in the side of the advance hydraulic chamber xadvfail is cleared to “0”.

Thereafter, the process goes to step 2129, wherein it is determined whether or not the first abnormality diagnosis deviation dvvtdg1 is less than a predetermined value K6 (for example, −5 deg or less). When the first abnormality diagnosis deviation dvvtdg1 is less than the predetermined value K6, since the VTC displacement angle vvt at a termination of the abnormality diagnosis changes excessively largely in the retard direction from the VTC displacement angle vvtret 0 at start of the abnormality diagnosis, it is determined that the one-way valve mechanism in the side of the retard hydraulic chamber 19 is in an open abnormality state and the process goes to step 2130. The open abnormality flag for the one-way valve mechanism in the side of the retard hydraulic chamber xretfail is set as “1”. On the other hand, when the first abnormality diagnosis deviation dvvtdg1 is greater than the predetermined value K6, the process goes to step 2131. The open abnormality flag for the one-way valve mechanism in the side of the retard hydraulic chamber xretfail is cleared to “0”.

Thereafter, the process goes to step 2132, wherein the abnormality diagnosis process end flag xdiagend is set as “1” which means the abnormality diagnosis process termination, and the present routine ends.

An example of an abnormality diagnosis in Embodiment 3 described above is shown in each of time charts in FIGS. 16 and 17. In the example of FIGS. 16 and 17, at time t1 a target displacement angle vvttgt changes in the advance direction and, based upon it, a VTC displacement angle vvt is feedback-controlled so as to change in the advance direction. In consequence, at a point where an absolute value of a deviation between the target displacement angle vvttgt and the VTC displacement angle vvt is less than a predetermined value and a predetermined holding operation execution condition is met, the holding operation starts and at the same time, the abnormality diagnosis process starts. During the executing of the holding operation (abnormality diagnosis), a control duty dutyvvt of the hydraulic control valve 21 is maintained to the pre-learned hold duty and also the target displacement angle vvttgt is maintained to be constant.

The example of FIG. 16 shows by a chain line a behavior of the VTC displacement angle vvt at the time of occurrence of the open abnormality state where the one-way valve mechanism in the side of the advance hydraulic chamber 18 remains to be opened. When the one-way valve mechanism in the side of the advance hydraulic chamber 18 is in an open abnormality state, since the hydraulic pressure in the side of the advance hydraulic chamber 18 where the open abnormality is occurring is leaked through the one-way valve mechanism to be reduced, the hydraulic pressure in the side of the retard hydraulic chamber 19 is higher than the hydraulic pressure in the side of the advance hydraulic chamber 18, creating the phenomenon that the VTC displacement angle vvt displaces in the retard direction.

Accordingly, in a case where the open abnormality of the hydraulic pressure in the side of the advance hydraulic chamber 18 occurs, at time t3 of the abnormality diagnosis termination the first abnormality diagnosis deviation dvvtdg1(=vvtret 0−vvt) as an abnormality diagnosis parameter evaluating a changing amount in the retard direction of the VTC displacement angle vvt during abnormality diagnosing is more than a predetermined value K5 (for example, 5 deg or more). As a result, it is determined that the one-way valve mechanism in the side of the advance hydraulic chamber 18 is in an open abnormality state and the open abnormality flag for the one-way valve mechanism in the side of the advance hydraulic chamber xadvfail is set as “1”. In this case, since the third abnormality deviation dvvtdg3 as an abnormality diagnosis parameter evaluating how much the vibration range of the VTC displacement angle during abnormality diagnosing displaces in the advance direction or in the retard direction is more than the predetermined value K3 (for example, 1 deg or more), it is determined that there does not occur the state where the one-way valve mechanisms in both of the side of the advance hydraulic chamber 18 and the side of the retard hydraulic chamber 19 are in an open abnormality state.

The example of FIG. 17 shows a behavior of the VTC displacement angle vvt when the one-way valve mechanisms in the side of the advance hydraulic chamber 18 and the side of the retard hydraulic chamber 19 are in an open abnormality state. When the one-way valve mechanisms in both the sides are in an open abnormality state, since a return of the VTC displacement angle vvt due to friction torque of the cam shaft occurs in a time relation to rotation of the cam shaft during holding operation, there occurs the phenomenon that the VTC displacement angle vvt relatively largely vibrates alternately in the advance direction and in the retard direction in a time relation to rotation of the cam shaft during holding operation centered at the target displacement angle vvttgt

Accordingly, in a case where the one-way valve mechanisms in both the sides are in an open abnormality state, since the third abnormality diagnosis deviation dvvtdg3 as the abnormality diagnosis parameter evaluating how much the vibration range of the VTC displacement angle during abnormality diagnosing displaces in the advance direction or in the retard direction is smaller than the predetermined value K3 (for example one degree) and also since the second abnormality diagnosis deviation dvvtdg2 as an abnormality diagnosis parameter evaluating the maximum margin of the vibration range of the VTC displacement angle vvt during abnormality diagnosing is more than the predetermined value K4 (for example 7 deg or more), it is determined that there occurs the state where the one-way valve mechanisms in both the sides are in an open abnormality state, setting the open abnormality flag xwopenfail for both the one-way valve mechanisms as “1”.

According to Embodiment 3 described above, it is determined whether or not the one-way valve mechanism in the side of the advance hydraulic chamber 18 or the retard hydraulic chamber 19 is in an open abnormality state based upon whether or not the first abnormality diagnosis deviation dvvtdg1(=vvtret0−vvt) as the abnormality diagnosis parameter evaluating a changing amount of the VTC displacement angle vvt within a predetermined period after start of the holding operation exceeds a normal range. Therefore, an open abnormality of the one-way valve mechanism in the side of the advance hydraulic chamber 18 or the retard hydraulic chamber 19 during engine operating can be quickly detected.

Yet, Embodiment 3 calculates a deviation (the maximum margin of the vibration range of the VTC displacement angle vvt) between the maximum value of the VTC displacement angle vvtmax and the minimum value of the VTC displacement angle vvtmin during abnormality diagnosing as a second abnormality diagnosis deviation dvvtdg2 and further, calculates a deviation between the maximum value of the VTC displacement angle vvtmax during abnormality diagnosing and the target displacement angle vvttgt (vvtmax−vvttgt) and also a deviation between the minimum value of the VTC displacement angle vvtmin and the target displacement angle vvttgt (vvtmin−vvttgt) and calculates an absolute value by addition of these two deviations as a third abnormality diagnosis deviation dvvtdg3. Since the third abnormality diagnosis deviation dvvtdg3 and the second abnormality diagnosis deviation dvvtdg2 are used as an abnormality diagnosis parameter evaluating a changing amount and a vibration range of the VTC displacement angle vvt during abnormality diagnosing, the open abnormality of the one-way valve mechanisms in both the sides and the open abnormality of the one-way valve mechanism in one side only can be distinguished and determined.

It should be noted that whether or not a changing amount or a vibration range of the VTC displacement angle vvt during abnormality diagnosing is within a normal range may be determined by comparing a deviation between the maximum value of the VTC displacement angle vvtmax during abnormality diagnosing and the target displacement angle vvttgt with a predetermined value or by comparing a deviation between the minimum value of the VTC displacement angle vvtmin during the abnormality diagnosing and the target displacement angle vvttgt with a predetermined value.

In addition, Embodiment 3 starts the abnormality diagnosis process at the same time with start of the holding operation, but may start the abnormality diagnosis process after a predetermined time elapses from start of the holding operation.

In addition, in the present invention, a hydraulic switching valve for switching the hydraulic pressure driving the drain switching valves 34 and 35 may be separated from the hydraulic control valve 21, but the present embodiment is so structured that the hydraulic switching valve is integral with the hydraulic control valve 21, and therefore, has an advantage of being capable of meeting the requirements such as reduction in the number of component parts, reduction in costs and downsizing.

Embodiment 4

When there occurs an open abnormality state where the drain switching valves 34 and 35 remain to be closed, even in a control region where it is required to drain oil from the hydraulic chambers 18 and 19 (it is required to discharge the hydraulic pressure) where the closed abnormality has occurred, the drain is blocked by the one-way valves 30 and 31. Therefore, it is difficult for the VTC displacement angle vvt to follow a change of the target displacement angle vvttgt and change in good response.

Considering this characteristic, Embodiment 4 of the present invention shown in FIGS. 21 to 23 is adapted to determine a convergent state of the VTC displacement angle to a target displacement angle vvttgt at a change of the target displacement angle vvttgt and determine whether or not there occurs the state where the drain switching valves 34 and 35 remain to be closed, based upon the convergent state.

Embodiment 4 measures at a change of the target displacement angle vvttgt a continuing time of the state where an absolute value of a deviation between a target displacement angle vvttgt and a VTC displacement angle vvt is more than a predetermined value K7 (for example, 4 deg or more) as data representing a convergent state, and determines whether or not the drain switching valves 34 and 35 are in a closed abnormality state, based upon whether or not this continuing time cvvtchkc exceeds a closed abnormality determination threshold value K8 (for example, 3000 ms). In this case, if the state where the VTC displacement angle vvt displaces in the retard direction relative to the target displacement angle vvttgt continues, it is determined that the drain switching valve 35 in the side of the retard hydraulic chamber 19 is in a closed abnormality state (abnormality state where it is difficult to advance due to no drain of the retard hydraulic chamber 19). If the state where the VTC displacement angle vvt displaces in the advance direction relative to the target displacement angle vvttgt continues, it is determined that the drain switching valve 35 in the side of the retard hydraulic chamber 19 is in a closed abnormality state (abnormality state where it is difficult to retard due to no drain of the advance hydraulic chamber 18).

The abnormality diagnosis process of Embodiment 4 described above is executed according to the abnormality diagnosis routine in FIGS. 21 and 22 by the ECU 43. The present routine is executed at each calculating timing of an engine rotational speed during engine operating (for example, every 180° CA in a case of a four-cylinder engine) and serves as abnormality diagnosis means. When the present routine is activated, first at step 2201 a target displacement angle vvttgt (target valve timing) in accordance with the present engine operating condition (engine rotational speed, intake pressure or the like) is calculated by a map or the like. After that, the process goes to step 2202, wherein an OCV current value (control duty dutyvvt) is feedback-controlled so that a deviation between the present VTC displacement angle vvt and the target displacement angle vvttgt becomes small.

Thereafter, the process goes to step 2203, wherein it is determined whether or not the VTC displacement control is during holding operating. When it is during holding operating, the abnormality diagnosis execution condition is not met and the process goes to step 2212, wherein a convergent time counter cvvtchkc is initialized to “0” and an advance deviation detection flag xadvjdg and a retard deviation detection flag xretjdg are cleared to “0”. Then, the present routine ends.

On the other hand, when it is determined at step 2203 that it is not during holding operating, the process goes to step 2204, wherein it is determined whether or not an absolute value |vvttgt−vvt| of a deviation between the present target displacement angle vvttgt and the VTC displacement angle vvt is greater than a predetermined value K7 (for example, 4 deg). As a result, when it is determined that the absolute value |vvttgt−vvt| of the deviation is less than the predetermined K7, it is determined that the convergent state of the VTC displacement angle vvt to the target displacement angle vvttgt is within a normal range and the process goes to step 2212, wherein the convergent time counter cvvtchkc is initialized and the advance deviation detection flag xadvjdg and the retard deviation detection flag xretjdg are cleared. Then, the present routine ends.

On the other hand, when it is determined at step 2204 that the absolute value |vvttgt−vvt| of the deviation is greater than the predetermined value K7, the process goes to step 2205, wherein whether or not the abnormality diagnosis execution condition is met is determined based upon whether or not .the following conditions (1) to (3) are all satisfied, for example.

-   -   (1) An engine rotational speed is more than a predetermined         rotational speed.     -   (2) An oil temperature of an engine (cooling water temperature)         is more than a predetermined temperature.     -   (3) A discharge hydraulic pressure of the oil pump 27 is more         than a predetermined value.

When any one of these three conditions (1) to (3) is not satisfied, it results in that the abnormality diagnosis execution condition is not met and the process goes to step 2212, wherein the convergent time counter cvvtchkc is initialized and the advance deviation detection flag xadvjdg and the retard deviation detection flag xretjdg are cleared. Then, the present routine ends.

On the other hand, when these three conditions (1) to (3) are all satisfied, it is determined that the abnormality diagnosis execution condition is met and the process goes to step 2206, wherein it is determined whether or not a deviation (vvttgt−vvt) of between the present target displacement angle vvttgt and the VTC displacement angle vvt is a plus value. When the deviation (vvttgt−vvt) is a plus value, it is determined that the present VTC displacement angle vvt displaces in the retard direction relative to the target displacement angle vvttgt and the process goes to step 2207, wherein it is determined whether or not the retard deviation detection flag xretjdg storing the deviation direction in the retard side of the previous VTC displacement angle vvt is “0” (that is, the deviation direction of the previous VTC displacement angle vvt is the advance direction). As a result, when it is determined that the retard deviation detection flag xretjdg is “0”, it is determined that the deviation direction of the VTC displacement angle vvt is reversed from the previous advance direction to the retard direction, and the process goes to step 2209, wherein the convergent time counter cvvtchkc is initialized and also the retard deviation detection flag xretjdg is set as “1” and the process goes to step 2211.

It should be noted that when the determination result at step 2207 is “No”, it is determined that the previous deviation direction and the present deviation direction of the VTC displacement angle vvt are the same retard direction, the process goes to step 2211 by skipping the process of step 2209.

On the other hand, at step 2206, when it is determined that a deviation (vvttgt−vvt) between the present target displacement angle vvttgt and the VTC displacement angle vvt is less than “0” (minus value), it is determined that the present VTC displacement angle vvt displaces in the advance direction relative to the target displacement angle vvttgt and the process goes to step 2208, wherein it is determined whether or not the advance deviation detection flag xadvjdg storing the deviation direction in the advance side of the previous VTC displacement angle vvt is “0” (that is, the deviation direction of the previous VTC displacement angle vvt is the retard direction). As a result, when it is determined that the advance deviation detection flag xadvjdg is “0”, it is determined that the deviation direction of the VTC displacement angle vvt is reversed from the previous retard direction to the advance direction, and the process goes to step 2210, wherein the convergent time counter cvvtchkc is initialized and also the advance deviation detection flag xadvjdg is set as “1” and the process goes to step 2211.

It should be noted that when the determination result at step 2208 is “No”, it is determined that the previous deviation direction and the present deviation direction of the VTC displacement angle vvt are the same advance direction, and the process goes to step 2211 by skipping the process of step 2210. At step 2211, it is determined whether or not the advance deviation detection flag xadvjdg and the retard deviation detection flag xretjdg both are “1”. When the advance deviation detection flag xadvjdg and the retard deviation detection flag xretjdg both are “1”, it is determined that the deviation of the advance direction and the deviation of the retard direction are reversed in one calculation cycle and the process goes to step 2212, wherein the convergent time counter cvvtchkc is initialized and the advance deviation detection flag xadvjdg and the retard deviation detection flag xretjdg are cleared. Then, the present routine ends.

When at step 2211, the determination result is “No”, it is determined that the deviation direction of the VTC displacement angle vvt is not reversed, and the process goes to step 2213 of FIG. 23, wherein the convergent time counter cvvtchkc measures a continuing time of the state where an absolute value of a deviation between a target displacement angle vvttgt and a VTC displacement angle vvt is more than a predetermined value K7 (for example, 4 deg or more) and it is determined whether or not any of the drain switching valves 34 and 35 is in a closed abnormality state, based upon whether or not this measurement time exceeds a closed abnormality determination threshold value K8 (for example, 300 ms). This convergent time counter cvvtchkc is a time counter for counting an elapse time after start of the abnormality diagnosis (after measurement start of the convergent state) by a time related process different from the present routine and is initialized by any one of steps 2209, 2210 and 2212.

When it is determined at step 2213 that the measurement time of the convergent time counter cvvtchkc does not reach the closed abnormality determination threshold value K8, the present routine ends as it is. Thereafter, at a point when the measurement time of the convergent time counter cvvtchkc has exceeded the closed abnormality determination threshold value K8, it is determined that any of the drain switching valves 34 and 35 is in a closed abnormality state, and the process goes to step 2214, wherein it is determined whether or not the deviation direction of the VTC displacement angle vvt is the retard direction based upon whether or not the retard deviation detection flag xretjdg is “1”. As a result, when it is determined that the retard deviation detection flag xretjdg is “1” (the deviation direction of the VTC displacement angle vvt is the retard direction), it is determined that the drain switching valve 35 in the side of the retard hydraulic chamber 19 is in a close abnormality state (abnormality state where it is difficult to advance due to no drain of the hydraulic pressure in the retard hydraulic chamber 19), and the process goes to step 2215, wherein a closed abnormality flag xretchkf of the drain switching valve in the side of the retard hydraulic chamber is set as “1”.

On the other hand, when it is determined that the retard deviation detection flag xretjdg is “0” (the deviation direction of the VTC displacement angle vvt is the advance direction), it is determined that the drain switching valve 34 in the side of the advance hydraulic chamber 18 is in a close abnormality state (abnormality state where it is difficult to retard due to no drain of the hydraulic pressure in the advance hydraulic chamber 18), and the process goes to step 2216, wherein a closed abnormality flag xadvchkf of the drain switching valve in the side of the advance hydraulic chamber is set as “1”.

Thereafter, the process goes to step 2217, wherein it is determined whether or not the closed abnormality flag xretchkf of the drain switching valve in the side of the retard hydraulic chamber and the closed abnormality flag xadvchkf of the drain switching valve in the side of the advance hydraulic chamber both are “1”. When the determination result is “No”, the present routine ends as it is and when the determination result is “Yes”, it is determined that the drain switching valves 34 and 35 in both of the side of the advance hydraulic chamber 18 and the side of the retard hydraulic chamber 19 are in a closed abnormality state, and the process goes to step 2218, wherein a closed abnormality flag xchkvaivef of both the drain switching valves is set as “1”, and the present routine ends.

An example of the abnormality diagnosis in Embodiment 4 described above is shown in a time chart of FIG. 21. In the example of FIG. 21, at time t1, a target displacement angle vvttgt is changed in the advance direction and, for following this change, a VTC displacement angle vvt is feedback-controlled so as to be changed in the advance direction. By such change of the target displacement angle vvttgt to the advance direction, at time t2 when a deviation between the target displacement angle vvttgt and the VTC displacement angle vvt is more than a predetermined value K7 (for example, 4 deg), the measurement operation of the convergent time counter cvvtchkc starts to measure a continuing time of a state where an absolute value of the deviation between the target displacement angle vvttgt and the VTC displacement angle vvt is more than the predetermined value K7.

During advance operating, the drain switching valve 35 in the side of the retard hydraulic chamber 19 is opened to drain oil from the retard hydraulic chamber 19, reducing the hydraulic pressure in the retard hydraulic chamber 19 and also to fill the oil into the advance hydraulic chamber 18, increasing the hydraulic pressure in the advance hydraulic chamber 18. Thereby, the VTC displacement angle vvt is controlled to be converged into the target displacement angle vvttgt in good response. Accordingly, when during advance operating, the drain switching valve 35 in the side of the retard hydraulic chamber 19 is normally opened, the continuing time of the state where then absolute value of the deviation between the target displacement angle vvttgt and the VTC displacement angle vvt is more than the predetermined value K7 (the measurement time t2 to t3 of the convergent time counter cvvtchkc) is smaller than a closed abnormality determination threshold value K8. In consequence, the closed abnormality flag xretchkf of the drain switching valve in the side of the retard hydraulic chamber is maintained to “0”.

In contrast, when the closed abnormality in the drain switching valve 35 in the side of the retard hydraulic chamber 19 occurs, it is difficult to advance due to no drain of the hydraulic pressure in the retard hydraulic chamber 19. Therefore, the continuing time of the state where then absolute value of the deviation between the target displacement angle vvttgt and the VTC displacement angle vvt is more than the predetermined value K7 (the measurement time of the convergent time counter cvvtchkc) is longer. At time t4 when the continuing time exceeds the closed abnormality determination threshold value K8, it is determined that the close abnormality in the drain switching valve 35 in the side of the retard hydraulic chamber 19 occurs, and the closed abnormality flag xretchkf of the drain switching valve in the side of the retard hydraulic chamber is maintained to “1”.

Embodiment 4 described above measures the continuing time of the state where the absolute value of the deviation between the target displacement angle vvttgt and the VTC displacement angle vvt is more than the predetermined value K7 as data representing the convergent state and determines whether or not the drain switching valves 34 and 35 are in a closed abnormality state, based upon whether or not this continuing time cvvtchkc exceeds the closed abnormality determination threshold value K8. Therefore. The closed abnormality of each of the drain switching valves 34 and 35 can be quickly detected during engine operating.

However, in a region where an engine rotational speed is low, the hydraulic pressure supplied to the hydraulic control valve 21 (discharge pressure of the oil pump 27) is reduced to deteriorate the response characteristic of the VTC displacement angle. As a result, it is unavoidable that the convergent characteristic of the VTC displacement angle to the target displacement angle is deteriorated.

In consideration of it, Embodiment 4 is adapted to determine the convergent state of the VTC displacement angle to the target displacement angle by assuming as a precondition (one of the abnormality diagnosis execution conditions) that the supply hydraulic pressure to the hydraulic control valve 21 is more than a predetermined value. Therefore, an erroneous determination of the convergent state at a low hydraulic pressure in a low rotational region, finally an erroneous determination of the closed abnormality is prevented beforehand, enabling an increase on accuracy and reliability of the abnormality diagnosis.

In this case, a hydraulic pressure sensor for detecting the supply hydraulic pressure to the hydraulic control valve 21 may be disposed, but Embodiment 4, considering that the hydraulic pressure supplied to the hydraulic control valve 21 (discharge pressure of the oil pump 27) changes with an engine rotational speed or an oil temperature (viscosity of operating oil), is adapted to determine whether or not the supply hydraulic pressure to the hydraulic control valve 21 is more than a predetermined value based upon information such as an engine rotational speed and/or an oil temperature (for example, a cooling water). In this way, since the supply hydraulic pressure to the hydraulic control valve 21 can be generally estimated by using information used in an engine control, it is not required to dispose a hydraulic pressure sensor for detecting the supply hydraulic pressure, thereby satisfying the demand for low costs.

It should be noted that Embodiment 4 described above measures the continuing time of the state where the absolute value of the deviation between the target displacement angle vvttgt and the VTC displacement angle vvt at a change of the target displacement angle is more than the predetermined value K7 as data representing the convergent state, but may measure, as data representing the convergent state, elapse time from a point where a deviation (absolute value) between the target displacement angle and the VTC displacement angle at a change of the target displacement angle is more than a first predetermined value until a point where the deviation (absolute value) is less than a second predetermined value smaller than the first predetermined value to determine presence/absence of the closed abnormality in each of the drain switching valves 34 and 35 based upon this elapse time.

The present invention may be carried out with various modifications within the spirit of the present invention, such as by a combination of the abnormality diagnosis process of Embodiment 3 and the abnormality diagnosis process of Embodiment 4 or a modification of a structure of the variable valve timing controller 11.

Embodiment 5

FIG. 24 shows Embodiment 5. Embodiment 5 differs in the following point from the variable valve timing controller shown in FIG. 1. It should be noted that components in FIG. 24 identical to those in FIG. 1 are referred to as the identical numbers.

First, the hydraulic control valve 21 in FIG. 1 drives the advance/retard hydraulic control valve 37 and the drain switching valve 38 by a single linear solenoid 36, but in FIG. 24, solenoids 36 and 51 are disposed in the advance/retard hydraulic control valve 37 and the drain switching valve 38 respectively and are respectively controlled by the ECU 43 and 52.

Embodiment 1 shown in FIG. 1 uses, as the drain switching valves 34 and 35, normally open-type switching valves, which are held in an open position by springs 41 and 42 when the hydraulic pressure is not applied to the drain switching valves 34 and 35. In contrast, in FIG. 24, when the hydraulic pressure is not applied to the drain switching valves 34 and 35, normally closed-type switching valves held in a closed open position by springs 41 and 42 are used as the drain switching valves 34 and 35. In consequence, the drain switching control function 38 is structured to supply the hydraulic pressure at the time of closing the drain switching valve, but in FIG. 24, is structured to stop the hydraulic pressure supply at the time of closing the drain switching valve.

In addition, in FIG. 1, the one-way valve and the drain switching valve are disposed in the hydraulic pressure supply passages corresponding to the advance hydraulic chamber and the retard hydraulic chamber in the single vane-accommodating chamber defined by a single vane, but in FIG. 24, the one-way valve and the drain switching valve are disposed in the hydraulic pressure supply passage corresponding to the advance hydraulic chamber in one vane-accommodating chamber and also in the hydraulic pressure supply passage corresponding to the retard hydraulic chamber in the other vane-accommodating chamber.

Embodiment 6

Regarding the structure of Embodiment 6, mainly difference points from FIG. 1 will be explained. It should be noted that components in FIG. 25 identical to those in FIG. 1 are referred to as the identical numbers.

In FIG. 1, two valves composed of a valve for switching a hydraulic passage for an advance/retard hydraulic control function and a valve for switching a hydraulic passage for a drain switching control function are provided. In contrast, in FIG. 25, a single valve achieves an advance/retard hydraulic control function and a drain switching control function. For this reason, the hydraulic pressure supply passages 28 and 29 are branched between the hydraulic control valve and the one-way valve and are in communication with the drain switching valves 34 and 35 respectively. 

1. A diagnosis device for a vane-type variable valve timing controller in which each of a plurality of vane accommodating chambers formed in a housing of the vane-type variable valve timing controller is divided into an advance hydraulic chamber and a retard hydraulic chamber by a vane comprising: a one-way valve disposed in each of a hydraulic supply passage of the advance hydraulic chamber and a hydraulic supply passage of the retard hydraulic chamber in at least one of the vane accommodating chambers for preventing reverse flow of operating oil from the each hydraulic chamber; a drain oil passage disposed in parallel to the hydraulic supply passage of the each hydraulic chamber for bypassing the one-way valve; a drain switching valve disposed in the each drain oil passage and driven by hydraulic pressure; and a hydraulic switching valve for switching the hydraulic pressure driving the each drain switching valve, wherein: during hold operating of holding a displacement angle of the variable valve timing controller (hereinafter, referred to as VTC displacement angle) to a target displacement angle, both the drain switching valves in a side of the advance hydraulic chamber and a side of the retard hydraulic chamber are closed to effectively function both the one-way valves in the side of the advance hydraulic chamber and the side of the retard hydraulic chamber; the hydraulic switching valve is controlled to prevent reverse flow of the operating oil from the each hydraulic chamber and also a control current of a hydraulic control valve controlling the hydraulic pressure in the each hydraulic chamber is controlled to a predetermined holding current; during advance/retard operating of displacing the VTC displacement angle to the advance direction or the retard direction, either one of the drain switching valves in the side of the advance hydraulic chamber and the side of the retard hydraulic chamber is opened in accordance with the displacement direction to control the hydraulic switching valve so that either one of the one-way valves does not operate; and the control current of the hydraulic control valve is controlled to vary the hydraulic pressure in the each hydraulic chamber, displacing the VTC displacement angle toward the target displacement angle, further comprising: abnormality diagnosis means adapted to determine presence/absence of abnormality in the advance/retard operation based upon a changing rate of the VTC displacement angle when a predetermined abnormality diagnosis execution condition is met during the advance/retard operating.
 2. A diagnosis device for a vane-type variable valve timing controller according to claim 1, wherein: at least one of abnormality diagnosis execution conditions is a condition that an engine rotational speed is in a low rotational region less than a predetermined rotational speed.
 3. A diagnosis device for a vane-type variable valve timing controller according to claim 1, wherein: at least one of abnormality diagnosis execution conditions is a condition that a deviation between the VTC displacement angle and the target displacement angle is more than a predetermined value.
 4. A diagnosis device for a vane-type variable valve timing controller according to claim 1, wherein: at least one of abnormality diagnosis execution conditions is a condition that a predetermined time elapses after the target displacement angle has changed.
 5. A diagnosis device for a vane-type variable valve timing controller according to claim 1, wherein: the abnormality diagnosis means determines presence/absence of the abnormality in the advance/retard operation in consideration of continuing time of a state where a changing rate of the VTC displacement angle is less than a predetermined value.
 6. A diagnosis device for a vane-type variable valve timing controller according to claim 1, wherein: the abnormality diagnosis means includes means for determining presence/absence of abnormality regarding the hydraulic control value and the hydraulic switching valve, wherein when the abnormality of the advance operation is detected, if it is determined that the hydraulic control valve and the hydraulic switching valve are normal, the means determines occurrence of a closed abnormality state where at least one of the drain switching valve in the side of the retard hydraulic chamber and the one-way valve in the side of the advance hydraulic chamber remains to be closed or an open abnormality state where at least one of the drain switching valve in the side of the advance hydraulic chamber and the one-way valve in the side of the advance hydraulic chamber remains to be opened; and wherein when the abnormality of the retard operation is detected, if it is determined that the hydraulic control valve and the hydraulic switching valve are normal, the means determines occurrence of a closed abnormality state where at least one of the drain switching valve in the side of the advance hydraulic chamber and the one-way valve in the side of the retard hydraulic chamber remains to be closed or an open abnormality state where at least one of the drain switching valve in the side of the retard hydraulic chamber and the one-way valve in the side of the retard hydraulic chamber remains to be opened.
 7. A diagnosis device for a vane-type variable valve timing controller according to claim 1, wherein: the hydraulic switching valve is integral with the hydraulic control valve.
 8. A diagnosis device for a vane-type variable valve timing controller in which each of a plurality of vane accommodating chambers formed in a housing of the vane-type variable valve timing controller is divided into an advance hydraulic chamber and a retard hydraulic chamber by a vane comprising: a first one-way valve disposed in a hydraulic supply passage of the advance hydraulic chamber in at least one of the vane accommodating chambers for preventing reverse flow of operating oil from the advance hydraulic chamber; a first drain control valve disposed in a first drain oil passage bypassing the first one-way valve and driven by hydraulic pressure; a second one-way valve disposed in a hydraulic supply passage of the retard hydraulic chamber in at least one of the vane accommodating chambers for preventing reverse flow of operating oil from the retard hydraulic chamber; a second drain control valve disposed in a second drain oil passage bypassing the second one-way valve and driven by the hydraulic pressure; a first hydraulic control valve for controlling the hydraulic pressure supplied to the variable valve timing controller; a second hydraulic control valve for controlling the hydraulic pressure driving the first and second drain control valves, wherein: during hold operating of holding a displacement angle of the variable valve timing controller (hereinafter, referred to as VTC displacement angle) to a target displacement angle, both the drain control valves in a side of the advance hydraulic chamber and a side of the retard hydraulic chamber are closed to effectively function both the one-way valves in the side of the advance hydraulic chamber and the side of the retard hydraulic chamber; the second hydraulic control valve is controlled to prevent reverse flow of the operating oil from the advance hydraulic chamber and the retard hydraulic chamber and also a control current of the first hydraulic control valve controlling the hydraulic pressure supplied to the variable valve timing controller is controlled to a predetermined holding current; during advance/retard operating of displacing the VTC displacement angle to the advance direction or the retard direction, either one of the drain control valves in the side of the advance hydraulic chamber and the side of the retard hydraulic chamber is opened in accordance with the displacement direction to control the second hydraulic control valve so that either one of the one-way valves does not operate; and the control current of the first hydraulic control valve is controlled to vary the hydraulic pressure supplied to the variable valve timing controller, displacing the VTC displacement angle toward the target displacement angle, further comprising: abnormality diagnosis means adapted to determine presence/absence of abnormality in the advance/retard operation based upon a changing rate of the VTC displacement angle when a predetermined abnormality diagnosis execution condition is met during the advance/retard operating.
 9. A diagnosis device for a vane-type variable valve timing controller according to claim 8, wherein: at least one of abnormality diagnosis execution conditions is a condition that an engine rotational speed is in a low rotational region less than a predetermined rotational speed.
 10. A diagnosis device for a vane-type variable valve timing controller according to claim 8, wherein: at least one of abnormality diagnosis execution conditions is a condition that a deviation between the VTC displacement angle and the target displacement angle is more than a predetermined value.
 11. A diagnosis device for a vane-type variable valve timing controller according to claim 8, wherein: at least one of abnormality diagnosis execution conditions is a condition that a predetermined time elapses after the target displacement angle has changed.
 12. A diagnosis device for a vane-type variable valve timing controller according to claim 8, wherein: the abnormality diagnosis means determines presence/absence of the abnormality in the advance/retard operation in consideration of continuing time of a state where a changing rate of the VTC displacement angle is less than a predetermined value.
 13. A diagnosis device for a vane-type variable valve timing controller according to claim 8, wherein: the abnormality diagnosis means includes means for determining presence/absence of the abnormality regarding the first hydraulic control value and the second hydraulic control valve, wherein when the abnormality of the advance operation is detected, if it is determined that the first hydraulic control valve and the second hydraulic control valve are normal, the means determines occurrence of a closed abnormality state where at least one of the drain switching valve in the side of the retard hydraulic chamber and the one-way valve in the side of the advance hydraulic chamber remains to be closed or an open abnormality state where at least one of the drain switching valve in the side of the advance hydraulic chamber and the one-way valve in the side of the advance hydraulic chamber remains to be opened; and wherein when the abnormality of the retard operation is detected, if it is determined that the first hydraulic control valve and the second hydraulic control valve are normal, the means determines occurrence of a closed abnormality state where at least one of the drain control valve in the side of the advance hydraulic chamber and the one-way valve in the side of the retard hydraulic chamber remains to be closed or an open abnormality state where at least one of the drain control valve in the side of the retard hydraulic chamber and the one-way valve in the side of the retard hydraulic chamber remains to be opened.
 14. A diagnosis device for a vane-type variable valve timing controller according to claim 8, wherein: a shaft for driving the first hydraulic control valve is integral with a shaft for driving the second hydraulic control valve.
 15. A diagnosis device for a vane-type variable valve timing controller in which each of a plurality of vane accommodating chambers formed in a housing of the vane-type variable valve timing controller is divided into an advance hydraulic chamber and a retard hydraulic chamber by a vane comprising: a first one-way valve disposed in a hydraulic supply passage of the advance hydraulic chamber in at least one of the vane accommodating chambers for preventing reverse flow of operating oil from the advance hydraulic chamber; a first drain control valve disposed in a first drain oil passage bypassing the first one-way valve and driven by hydraulic pressure; a second one-way valve disposed in a hydraulic supply passage of the retard hydraulic chamber in at least one of the vane accommodating chambers for preventing reverse flow of operating oil from the retard hydraulic chamber; a second drain control valve disposed in a second drain oil passage bypassing the second one-way valve and driven by the hydraulic pressure; a single first hydraulic control valve for controlling the hydraulic pressure supplied to the first and second drain control valves and the variable valve timing controller; wherein: during hold operating of holding a displacement angle of the variable valve timing controller (hereinafter, referred to as VTC displacement angle) to a target displacement angle, a control current of the hydraulic control valve is controlled to a predetermined holding current to close both the drain control valves in a side of the advance hydraulic chamber and a side of the retard hydraulic chamber to effectively function both the one-way valves in the side of the advance hydraulic chamber and the side of the retard hydraulic chamber; thereby preventing reverse flow of the operating oil from the advance hydraulic chamber and the retard hydraulic chamber and also controlling the hydraulic pressure supplied to the variable valve timing controller; during advance/retard operating of displacing the VTC displacement angle to the advance direction or the retard direction, the control current of the hydraulic control valve is controlled to open either one of the drain control valves in a side of the advance hydraulic chamber and a side of the retard hydraulic chamber in accordance with the displacement direction so that either one of the one-way valves does not operate; and further, the hydraulic pressure supplied to the variable valve timing controller is varied, thereby displacing the VTC displacement angle toward the target displacement angle, further comprising: abnormality diagnosis means adapted to determine presence/absence of abnormality in the advance/retard operation based upon a changing rate of the VTC displacement angle when a predetermined abnormality diagnosis execution condition is met during the advance/retard operating.
 16. A diagnosis device for a vane-type variable valve timing controller according to claim 15, wherein: at least one of abnormality diagnosis execution conditions is a condition that an engine rotational speed is in a low rotational region less than a predetermined rotational speed.
 17. A diagnosis device for a vane-type variable valve timing controller according to claim 15, wherein: at least one of abnormality diagnosis execution conditions is a condition that a deviation between the VTC displacement angle and the target displacement angle is more than a predetermined value.
 18. A diagnosis device for a vane-type variable valve timing controller according to claim 15, wherein: at least one of abnormality diagnosis execution conditions is a condition that a predetermined time elapses after the target displacement angle has changed.
 19. A diagnosis device for a vane-type variable valve timing controller according to claim 15, wherein: the abnormality diagnosis means determines presence/absence of the abnormality in the advance/retard operation in consideration of continuing time of a state where a changing rate of the VTC displacement angle is less than a predetermined value.
 20. A diagnosis device for a vane-type variable valve timing controller according to claim 15, wherein: the abnormality diagnosis means includes means for determining presence/absence of the abnormality regarding the hydraulic control value, wherein when the abnormality of the advance operation is detected, if it is determined that the hydraulic control valve is normal, the means determines occurrence of a closed abnormality state where at least one of the drain control valve in the side of the retard hydraulic chamber and the one-way valve in the side of the advance hydraulic chamber remains to be closed or an open abnormality state where at least one of the drain control valve in the side of the advance hydraulic chamber and the one-way valve in the side of the advance hydraulic chamber remains to be opened; and wherein when the abnormality of the retard operation is detected, if it is determined that the hydraulic control valve is normal, the means determines occurrence of a closed abnormality state where at least one of the drain control valve in the side of the advance hydraulic chamber and the one-way valve in the side of the retard hydraulic chamber remains to be closed or an open abnormality state where at least one of the drain control valve in the side of the retard hydraulic chamber and the one-way valve in the side of the retard hydraulic chamber remains to be opened.
 21. A diagnosis device for a vane-type variable valve timing controller in which each of a plurality of vane accommodating chambers formed in a housing of the vane-type variable valve timing controller is divided into an advance hydraulic chamber and a retard hydraulic chamber by a vane comprising: a one-way valve disposed in each of a hydraulic supply passage of the advance hydraulic chamber and a hydraulic supply passage of the retard hydraulic chamber in at least one of the vane accommodating chambers for preventing reverse flow of operating oil from the each hydraulic chamber; a drain oil passage disposed in parallel to the hydraulic supply passage of the each hydraulic chamber for bypassing the one-way valve; a drain switching valve disposed in the each drain oil passage and driven by hydraulic pressure; and a hydraulic switching valve for switching the hydraulic pressure driving the each drain switching valve, wherein: during hold operating of holding a displacement angle of the variable valve timing controller (hereinafter, referred to as VTC displacement angle) to a target displacement angle, both the drain switching valves in a side of the advance hydraulic chamber and a side of the retard hydraulic chamber are closed to effectively function both the one-way valves in the side of the advance hydraulic chamber and the side of the retard hydraulic chamber; thereby, the hydraulic switching valve is controlled to prevent reverse flow of the operating oil from both the hydraulic chambers and also a control current of the hydraulic control valve controlling the hydraulic pressure in the each hydraulic chamber is controlled to a predetermined holding current; during advance/retard operating of displacing the VTC displacement angle to the advance direction or the retard direction, either one of the drain switching valves in a side of the advance hydraulic chamber and a side of the retard hydraulic chamber is opened in accordance with the displacement direction to control the hydraulic switching valve so that either one of the one-way valves does not operate; and the control current of the hydraulic control valve is controlled to vary the hydraulic pressure in the each hydraulic chamber, displacing the VTC displacement angle toward the target displacement angle, further comprising: when at the time of meeting a predetermined abnormality diagnosis execution condition during the advance/retard operating, the holding current is vibrated in a predetermined amplitude, abnormality diagnosis means adapted to determine presence/absence of the abnormality in at least one of the drain switching valve and the one-way valve based upon a changing degree of the VTC displacement angle due to the vibration of the holding current.
 22. A diagnosis device for a vane-type variable valve timing controller according to claim 21, wherein: the hydraulic switching valve is integral with the hydraulic control valve.
 23. A diagnosis device for a vane-type variable valve timing controller according to claim 21, wherein: the abnormality diagnosis means sets an amplitude and a cycle in the vibration of the holding current so that a changing degree of the VTC displacement angle at a normal operation is within a range of an allowance changing amount in the VTC displacement angle during a usual holding operating.
 24. A diagnosis device for a vane-type variable valve timing controller according to claim 21, wherein: the abnormality diagnosis means sets an amplitude in the vibration of the holding current so that a changing amount of the VTC displacement angle due to an increasing direction amplitude of the holding current is substantially equal to a changing amount in the VTC displacement angle due to a decreasing direction amplitude thereof.
 25. A diagnosis device for a vane-type variable valve timing controller according to claim 21, wherein: the abnormality diagnosis means sets a cycle in the vibration of the holding current close to the minimum time of being capable of transmitting the hydraulic pressure to the each hydraulic chamber in an increasing direction amplitude and a decreasing direction amplitude of the holding current in consideration of a delay of a hydraulic transmission system to the each hydraulic chamber.
 26. A diagnosis device for a vane-type variable valve timing controller according to claim 21, wherein: the abnormality diagnosis means starts the vibration of the holding current after a predetermined time elapses from start of the holding operation and determines presence/absence of the abnormality by performing the vibration of the holding current for a predetermine time.
 27. A diagnosis device for a vane-type variable valve timing controller according to claim 21, further comprising: holding current learning means for learning the holding current, wherein: the abnormality diagnosis means vibrates the holding current centered at a holding current learning value learned by the holding current learning means.
 28. A diagnosis device for a vane-type variable valve timing controller according to claim 21, wherein: the each drain switching valve is structured in such a manner as to be all the time opened in a region of a high rotational side where an engine generated hydraulic pressure is high; and in a region of a low rotational side where both of the drain switching valves are closed, the abnormality diagnosis means determines whether or not there occurs an open abnormality state where at least one of the drain switching valve and the one-way valve in the side of the advance hydraulic chamber or the retard hydraulic chamber remains to be opened, based upon whether or not a changing degree of the VTC displacement angle exceeds a predetermined abnormality determination threshold value to increase in an advance or a retard direction, and in a region of a high rotational side where both of the drain switching valves are opened, the abnormality diagnosis means determines whether or not there occurs a closed abnormality state where the drain switching valve in the side of the advance hydraulic chamber or the retard hydraulic chamber remains to be closed, based upon whether or not a changing degree of the VTC displacement angle exceeds a predetermined abnormality determination threshold value to increase in an advance or a retard direction.
 29. A diagnosis device for a vane-type variable valve timing controller in which each of a plurality of vane accommodating chambers formed in a housing of the vane-type variable valve timing controller is divided into an advance hydraulic chamber and a retard hydraulic chamber by a vane comprising: a first one-way valve disposed in a hydraulic supply passage of the advance hydraulic chamber in at least one of the vane accommodating chambers for preventing reverse flow of operating oil from the advance hydraulic chamber; a first drain control valve disposed in a first drain oil passage bypassing the first one-way valve and driven by hydraulic pressure; a second one-way valve disposed in a hydraulic supply passage of the retard hydraulic chamber in at least one of the vane accommodating chambers for preventing reverse flow of operating oil from the retard hydraulic chamber; a second drain control valve disposed in a second drain oil passage bypassing the second one-way valve and driven by the hydraulic pressure; a first hydraulic control valve for controlling the hydraulic pressure supplied to the variable valve timing controller; a second hydraulic control valve for controlling the hydraulic pressure driving the first and second drain control valves, wherein: during hold operating of holding a displacement angle of the variable valve timing controller (hereinafter, referred to as VTC displacement angle) to a target displacement angle, both the drain control valves in a side of the advance hydraulic chamber and a side of the retard hydraulic chamber are closed to effectively function both the one-way valves in the side of the advance hydraulic chamber and the side of the retard hydraulic chamber; thereby, the second hydraulic control valve is controlled to prevent reverse flow of the operating oil from the advance hydraulic chamber and the retard hydraulic chamber and also a control current of the first hydraulic control valve controlling the hydraulic pressure supplied to the variable valve timing controller is controlled to a predetermined holding current; during advance/retard operating of displacing the VTC displacement angle to the advance direction or the retard direction, either one of the drain control valves in the side of the advance hydraulic chamber and the side of the retard hydraulic chamber is opened in accordance with the displacement direction to control the second hydraulic control valve so that either one of the one-way valves does not operate; and the control current of the first hydraulic control valve is controlled to vary the hydraulic pressure supplied to the variable valve timing controller, displacing the VTC displacement angle toward the target displacement angle, further comprising: when at the time of meeting a predetermined abnormality diagnosis execution condition during the advance/retard operating, the holding current is vibrated in a predetermined amplitude, abnormality diagnosis means adapted to determine presence/absence of abnormality in at least one of the drain control valve and the one-way valve based upon a changing rate of the VTC displacement angle due to the vibration of the holding current.
 30. A diagnosis device for a vane-type variable valve timing controller according to claim 29, wherein: a shaft for driving the first hydraulic control valve is integral with a shaft for driving the second hydraulic control valve.
 31. A diagnosis device for a vane-type variable valve timing controller according to claim 29, wherein: the abnormality diagnosis means sets an amplitude and a cycle in the vibration of the holding current so that a changing degree of the VTC displacement angle at a normal operation is within a range of an allowance changing amount in the VTC displacement angle during a usual holding operating.
 32. A diagnosis device for a vane-type variable valve timing controller according to claim 29, wherein: the abnormality diagnosis means sets an amplitude in the vibration of the holding current so that a changing amount of the VTC displacement angle due to an increasing direction amplitude of the holding current is substantially equal to a changing amount in the VTC displacement angle due to a decreasing direction amplitude thereof
 33. A diagnosis device for a vane-type variable valve timing controller according to claim 29, wherein: the abnormality diagnosis means sets a cycle in the vibration of the holding current close to the minimum time of being capable of transmitting the hydraulic pressure to the each hydraulic chamber in an increasing direction amplitude and a decreasing direction amplitude of the holding current in consideration of a delay of a hydraulic transmission system supplying the hydraulic pressure to the variable valve timing controller.
 34. A diagnosis device for a vane-type variable valve timing controller according to claim 29, wherein: the abnormality diagnosis means starts the vibration of the holding current after a predetermined time elapses from start of the holding operation and determines presence/absence of the abnormality by performing the vibration of the holding current for a predetermine time.
 35. A diagnosis device for a vane-type variable valve timing controller according to claim 29, further comprising: holding current learning means for learning the holding current, wherein: the abnormality diagnosis means vibrates the holding current centered at a holding current learning value learned by the holding current learning means.
 36. A diagnosis device for a vane-type variable valve timing controller according to claim 29, wherein: the each drain control valve is structured in such a manner as to be all the time opened in a region of a high rotational side where an engine generated hydraulic pressure is high; and in a region of a low rotational side where both of the drain control valves are closed at a normal operation, the abnormality diagnosis means determines whether or not there occurs an open abnormality state where at least one of the drain control valve and the one-way valve in the side of the advance hydraulic chamber or the retard hydraulic chamber remains to be opened, based upon whether or not a changing degree of the VTC displacement angle exceeds a predetermined abnormality determination threshold value to increase in an advance or a retard direction, and in a region of a high rotational side where both of the drain control valves are opened at a normal operation, the abnormality diagnosis means determines whether or not there occurs a closed abnormality state where the drain control valve in the side of the advance hydraulic chamber or the retard hydraulic chamber remains to be closed, based upon whether or not a changing degree of the VTC displacement angle exceeds a predetermined abnormality determination threshold value to increase in an advance or a retard direction.
 37. A diagnosis device for a vane-type variable valve timing controller in which each of a plurality of vane accommodating chambers formed in a housing of the vane-type variable valve timing controller is divided into an advance hydraulic chamber and a retard hydraulic chamber by a vane comprising: a first one-way valve disposed in a hydraulic supply passage of the advance hydraulic chamber in at least one of the vane accommodating chambers for preventing reverse flow of operating oil from the advance hydraulic chamber; a first drain control valve disposed in a first drain oil passage bypassing the first one-way valve and driven by hydraulic pressure; a second one-way valve disposed in a hydraulic supply passage of the retard hydraulic chamber in at least one of the vane accommodating chambers for preventing reverse flow of operating oil from the retard hydraulic chamber; a second drain control valve disposed in a second drain oil passage bypassing the second one-way valve and driven by the hydraulic pressure; a single first hydraulic control valve for controlling the hydraulic pressure supplied to the first and second drain control valves and the variable valve timing controller; wherein: during holding operating of holding a displacement angle of the variable valve timing controller (hereinafter, referred to as VTC displacement angle) to a target displacement angle, a control current of the hydraulic control valve is controlled to a predetermined holding current to close both the drain control valves in a side of the advance hydraulic chamber and a side of the retard hydraulic chamber to effectively function both the one-way valves in the side of the advance hydraulic chamber and the side of the retard hydraulic chamber; thereby preventing reverse flow of the operating oil from the advance hydraulic chamber and the retard hydraulic chamber and also controlling the hydraulic pressure supplied to the variable valve timing controller; during advance/retard operating of displacing the VTC displacement angle to the advance direction or the retard direction, the control current of the hydraulic control valve is controlled to open either one of the drain control valves in the side of the advance hydraulic chamber and the side of the retard hydraulic chamber in accordance with the displacement direction so that either one of the one-way valves does not operate; and further, the hydraulic pressure supplied to the variable valve timing controller is varied, thereby displacing the VTC displacement angle toward the target displacement angle, further comprising: when at the time of meeting a predetermined abnormality diagnosis execution condition during the advance/retard operating, the holding current is vibrated in a predetermined amplitude, abnormality diagnosis means adapted to determine presence/absence of abnormality in at least one of the drain control valve and the one-way valve based upon a changing degree of the VTC displacement angle due to the vibration of the holding current.
 38. A diagnosis device for a vane-type variable valve timing controller according to claim 37, wherein: the abnormality diagnosis means sets an amplitude and a cycle in the vibration of the holding current so that a changing degree of the VTC displacement angle at a normal operation is within a range of an allowance changing amount in the VTC displacement angle during a usual holding operating.
 39. A diagnosis device for a vane-type variable valve timing controller according to claim 37, wherein: the abnormality diagnosis means sets an amplitude in the vibration of the holding current so that a changing amount of the VTC displacement angle due to an increasing direction amplitude of the holding current is substantially equal to a changing amount in the VTC displacement angle due to a decreasing direction amplitude thereof
 40. A diagnosis device for a vane-type variable valve timing controller according to claim 37, wherein: the abnormality diagnosis means sets a cycle in the vibration of the holding current close to the minimum time of being capable of transmitting the hydraulic pressure to the each hydraulic chamber in an increasing direction amplitude and a decreasing direction amplitude of the holding current in consideration of a delay of a hydraulic transmission system supplying the hydraulic pressure to the variable valve timing controller.
 41. A diagnosis device for a vane-type variable valve timing controller according to claim 37, wherein: the abnormality diagnosis means starts the vibration of the holding current after a predetermined time elapses from start of the holding operation and determines presence/absence of the abnormality by performing the vibration of the holding current for a predetermine time.
 42. A diagnosis device for a vane-type variable valve timing controller according to claim 37, further comprising: holding current learning means for learning the holding current, wherein: the abnormality diagnosis means vibrates the holding current centered at a holding current learning value learned by the holding current learning means.
 43. A diagnosis device for a vane-type variable valve timing controller according to claim 37, wherein: the each drain control valve is structured in such a manner as to be all the time opened in a region of a high rotational side where an engine generated hydraulic pressure is high; and in a region of a low rotational side where both of the drain control valves are closed at a normal operation, the abnormality diagnosis means determines whether or not there occurs an open abnormality state where at least one of the drain control valve and the one-way valve in the side of the advance hydraulic chamber or the retard hydraulic chamber remains to be opened based upon whether or not a changing degree of the VTC displacement angle exceeds a predetermined abnormality determination threshold value to increase in an advance or a retard direction, and in a region of a high rotational side where both of the drain control valves are opened at a normal operation, the abnormality diagnosis means determines whether or not there occurs a closed abnormality state where the drain control valve in the side of the advance hydraulic chamber or the retard hydraulic chamber remains to be closed based upon whether or not a changing degree of the VTC displacement angle exceeds a predetermined abnormality determination threshold value to increase in an advance or retard direction.
 44. A diagnosis device for a vane-type variable valve timing controller in which each of a plurality of vane accommodating chambers formed in a housing of the vane-type variable valve timing controller is divided into an advance hydraulic chamber and a retard hydraulic chamber by a vane comprising: a one-way valve disposed in each of a hydraulic supply passage of the advance hydraulic chamber and a hydraulic supply passage of the retard hydraulic chamber in at least one of the vane accommodating chambers for preventing reverse flow of operating oil from the each hydraulic chamber; a drain oil passage disposed in parallel to the hydraulic supply passage of the each hydraulic chamber for bypassing the one-way valve; a drain switching valve disposed in the each drain oil passage and driven by hydraulic pressure; and a hydraulic switching valve switching the hydraulic pressure driving the each drain switching valve, wherein: during hold operating of holding a displacement angle of the variable valve timing controller (hereinafter, referred to as VTC displacement angle) to a target displacement angle, both the drain switching valves in a side of the advance hydraulic chamber and a side of the retard hydraulic chamber are closed to effectively function both the one-way valves in the side of the advance hydraulic chamber and the side of the retard hydraulic chamber; thereby, the hydraulic switching valve is controlled to prevent reverse flow of the operating oil from both the hydraulic chambers and also a control current of the hydraulic control valve controlling the hydraulic pressure in the each hydraulic chamber is controlled to a predetermined holding current; during advance/retard operating of displacing the VTC displacement angle to the advance direction or the retard direction, either one of the drain switching valves in the side of the advance hydraulic chamber and the of the retard hydraulic chamber side is opened in accordance with the displacement direction to control the hydraulic switching valve so that either one of the one-way valves does not operate; and further, the control current of the hydraulic control valve is controlled to vary the hydraulic pressure in the each hydraulic chamber, displacing the VTC displacement angle toward the target displacement angle, further comprising: abnormality diagnosis means adapted to determine whether or not there occurs an open abnormality state where at least one of the drain switching valve and the one-way valve remains to be opened, based upon a changing amount of the VTC displacement angle within a predetermined period during the holding operating.
 45. A diagnosis device for a vane-type variable valve timing controller according to claim 44, wherein: the abnormality diagnosis means calculates a difference between a VTC displacement angle immediately after start of the holding operation and a VTC displacement angle at elapse of the predetermined period to determine presence/absence of the open abnormality state in at least one of the drain switching valve and the one-way valve based upon this difference.
 46. A diagnosis device for a vane-type variable valve timing controller according to claim 44, wherein: the abnormality diagnosis means detects a maximum value and a minimum value of a VTC displacement angle from a point immediately after start of the holding operation until a point at elapse of the predetermined period to calculate a difference between the maximum value and the minimum value, determining presence/absence of the open abnormality state in at least one of the drain switching valve and the one-way valve based upon this difference.
 47. A diagnosis device for a vane-type variable valve timing controller according to claim 44, wherein: the abnormality diagnosis means detects a maximum value and a minimum value of a VTC displacement angle from a point immediately after start of the holding operation until a point at elapse of the predetermined period to calculate a deviation between a target displacement angle during the holding operating and the maximum value and a deviation between the target displacement angle and the minimum value, determining presence/absence of the open abnormality state in at least one of the drain switching valve and the one-way valve based upon these two deviations.
 48. A diagnosis device for a vane-type variable valve timing controller in which each of a plurality of vane accommodating chambers formed in a housing of the vane-type variable valve timing controller is divided into an advance hydraulic chamber and a retard hydraulic chamber by a vane comprising: a one-way valve disposed in each of a hydraulic supply passage of the advance hydraulic chamber and a hydraulic supply passage of the retard hydraulic chamber in at least one of the vane accommodating chambers for preventing reverse flow of operating oil from the each hydraulic chamber; a drain oil passage disposed in parallel to the hydraulic supply passage of the each hydraulic chamber for bypassing the one-way valve; a drain switching valve disposed in the each drain oil passage and driven by hydraulic pressure; and a hydraulic switching valve for switching the hydraulic pressure driving the each drain switching valve, wherein: during hold operating of holding a displacement angle of the variable valve timing controller (hereinafter, referred to as VTC displacement angle) to a target displacement angle, both the drain switching valves in a side of the advance hydraulic chamber and a side of the retard hydraulic chamber are closed to effectively function both the one-way valves in the side of the advance hydraulic chamber and the side of the retard hydraulic chamber; thereby, the hydraulic switching valve is controlled to prevent reverse flow of the operating oil from both the hydraulic chambers and also a control current of the hydraulic control valve controlling the hydraulic pressure in the each hydraulic chamber is controlled to a predetermined holding current; during advance/retard operating of displacing the VTC displacement angle to the advance direction or the retard direction, either one of the drain switching valves in the side of the advance hydraulic chamber and the side of the retard hydraulic chamber side is opened in accordance with the displacement direction to control the hydraulic switching valve so that either one of the one-way valves does not operate; and further, the control current of the hydraulic control valve is controlled to vary the hydraulic pressure in the each hydraulic chamber, displacing the VTC displacement angle toward the target displacement angle, further comprising: abnormality diagnosis means determines a convergent state to the target displacement angle of the VTC displacement angle at changing the target displacement angle to determine whether or not there occurs a closed abnormality state where the drain switching valve remains to be closed, based upon the convergent state.
 49. A diagnosis device for a vane-type variable valve timing controller according to claim 48, wherein: the abnormality diagnosis means measures, as data representing the convergent state, continuing time of a state where a deviation between the target displacement angle and the VTC displacement angle is more than a predetermined value to determine presence/absence of the closed abnormality state in the drain switching valve based upon this continuing time.
 50. A diagnosis device for a vane-type variable valve timing controller according to claim 48, wherein: the abnormality diagnosis means measures, as data representing the convergent state, elapse time from a point where a deviation between the target displacement angle and the VTC displacement angle is more than a first predetermined value until a point where the deviation is less than a second predetermined value smaller than the first predetermined value to determine presence/absence of the closed abnormality state in the drain switching valve based upon this elapse time.
 51. A diagnosis device for a vane-type variable valve timing controller according to claim 48, wherein: the abnormality diagnosis means determines the convergent state by setting as a precondition that a supply hydraulic pressure to the hydraulic control valve is more than a predetermined value.
 52. A diagnosis device for a vane-type variable valve timing controller according to claim 51, wherein: the abnormality diagnosis means determines whether or not the supply hydraulic pressure to the hydraulic control valve is more than the predetermined value, based upon information regarding at least one of an engine rotational speed and an oil temperature.
 53. A diagnosis device for a vane-type variable valve timing controller according to claim 44, wherein: the hydraulic switching valve is integral with the hydraulic control valve.
 54. A diagnosis device for a vane-type variable valve timing controller in which each of a plurality of vane accommodating chambers formed in a housing of the vane-type variable valve timing controller is divided into an advance hydraulic chamber and a retard hydraulic chamber by a vane comprising: a first one-way valve disposed in a hydraulic supply passage of the advance hydraulic chamber in at least one of the vane accommodating chambers for preventing reverse flow of operating oil from the advance hydraulic chamber; a first drain control valve disposed in a first drain oil passage bypassing the first one-way valve and driven by hydraulic pressure; a second one-way valve disposed in a hydraulic supply passage of the retard hydraulic chamber in at least one of the vane accommodating chambers for preventing reverse flow of operating oil from the retard hydraulic chamber; a second drain control valve disposed in a second drain oil passage bypassing the second one-way valve and driven by hydraulic pressure; a first hydraulic control valve for controlling the hydraulic pressure supplied to the variable valve timing controller; a second hydraulic control valve for controlling the hydraulic pressure driving the first and second drain control valves, wherein: during hold operating of holding a displacement angle of the variable valve timing controller (hereinafter, referred to as VTC displacement angle) to a target displacement angle, both the drain control valves in a side of the advance hydraulic chamber and a side of the retard hydraulic chamber are closed to effectively function both the one-way valves in the side of the advance hydraulic chamber and the side of the retard hydraulic chamber; thereby, the second hydraulic control valve is controlled to prevent reverse flow of the operating oil from the advance hydraulic chamber and the retard hydraulic chamber and also a control current of the first hydraulic control valve controlling the hydraulic pressure supplied to the variable valve timing controller is controlled to a predetermined holding current; during advance/retard operating of displacing the VTC displacement angle to the advance direction or the retard direction, either one of the drain control valves in the side of the advance hydraulic chamber and the side of the retard hydraulic chamber is opened in accordance with the displacement direction to control the second hydraulic control valve so that either one of the one-way valves does not operate; and further, the control current of the first hydraulic control valve is controlled to vary the hydraulic pressure supplied to the variable valve timing controller, displacing the VTC displacement angle toward the target displacement angle, further comprising: abnormality diagnosis means adapted to determine whether or not there occurs an open abnormality state where at least one of the drain control valve and the one-way valve remains to be opened, based upon a changing amount of the VTC displacement angle within a predetermined period during the holding operating.
 55. A diagnosis device for a vane-type variable valve timing controller according to claim 54, wherein: the abnormality diagnosis means calculates a difference between a VTC displacement angle immediately after start of the holding operation and a VTC displacement angle at elapse of the predetermined period to determine presence/absence of the open abnormality state in at least one of the drain control valve and the one-way valve based upon this difference.
 56. A diagnosis device for a vane-type variable valve timing controller according to claim 54, wherein: the abnormality diagnosis means detects a maximum value and a minimum value of a VTC displacement angle from a point immediately after start of the holding operation until a point at elapse of the predetermined period to calculate a difference between the maximum value and the minimum value, determining presence/absence of the open abnormality state in at least one of the drain control valve and the one-way valve based upon this difference.
 57. A diagnosis device for a vane-type variable valve timing controller according to claim 54, wherein: the abnormality diagnosis means detects a maximum value and a minimum value of a VTC displacement angle from a point immediately after start of the holding operation until a point at elapse of the predetermined period to calculate a deviation between a target displacement angle during the holding operating and the maximum value and a deviation between the target displacement angle and the minimum value, determining presence/absence of the open abnormality state in at least one of the drain control valve and the one-way valve based upon these two deviations.
 58. A diagnosis device for a vane-type variable valve timing controller in which each of a plurality of vane accommodating chambers formed in a housing of the vane-type variable valve timing controller is divided into an advance hydraulic chamber and a retard hydraulic chamber by a vane comprising: a first one-way valve disposed in a hydraulic supply passage of the advance hydraulic chamber in at least one of the vane accommodating chambers for preventing reverse flow of operating oil from the advance hydraulic chamber; a first drain control valve disposed in a first drain oil passage bypassing the first one-way valve and driven by hydraulic pressure; a second one-way valve disposed in a hydraulic supply passage of the retard hydraulic chamber in at least one of the vane accommodating chambers for preventing reverse flow of operating oil from the retard hydraulic chamber; a second drain control valve disposed in a second drain oil passage bypassing the second one-way valve and driven by the hydraulic pressure; a first hydraulic control valve for controlling the hydraulic pressure supplied to the variable valve timing controller; a second hydraulic control valve for controlling the hydraulic pressure driving the first and second drain control valves, wherein: during hold operating of holding a displacement angle of the variable valve timing controller (hereinafter, referred to as VTC displacement angle) to a target displacement angle, both the drain control valves in a side of the advance hydraulic chamber and a side of the retard hydraulic chamber are closed to effectively function both the one-way valves in the side of the advance hydraulic chamber and the side of the retard hydraulic chamber; thereby, the second hydraulic control valve is controlled to prevent reverse flow of the operating oil from the advance hydraulic chamber and the retard hydraulic chamber and also a control current of the first hydraulic control valve controlling the hydraulic pressure supplied to the variable valve timing controller is controlled to a predetermined holding current; during advance/retard operating of displacing the VTC displacement angle to the advance direction or the retard direction, either one of the drain control valves in the side of the advance hydraulic chamber and the side of the retard hydraulic chamber is opened in accordance with the displacement direction to control the second hydraulic control valve so that either one of the one-way valves does not operate; and further, the control current of the first hydraulic control valve is controlled to vary the hydraulic pressure supplied to the variable valve timing controller, displacing the VTC displacement angle toward the target displacement angle, further comprising: abnormality diagnosis means determines a convergent state to the target displacement angle of the VTC displacement angle at changing the target displacement angle to determine whether or not there occurs a closed abnormality state where the drain control valve remains to be closed, based upon the convergent state.
 59. A diagnosis device for a vane-type variable valve timing controller according to claim 58, wherein: the abnormality diagnosis means measures, as data representing the convergent state, continuing time of a state where a deviation between the target displacement angle and the VTC displacement angle is more than a predetermined value to determine presence/absence of the closed abnormality state in the drain control valve based upon this continuing time.
 60. A diagnosis device for a vane-type variable valve timing controller according to claim 58, wherein: the abnormality diagnosis means measures, as data representing the convergent state, elapse time from a point where a deviation between the target displacement angle and the VTC displacement angle is more than a first predetermined value until a point where the deviation is less than a second predetermined value smaller than the first predetermined value to determine presence/absence of the closed abnormality state in the drain control valve based upon this elapse time.
 61. A diagnosis device for a vane-type variable valve timing controller according to claim 58, wherein: the abnormality diagnosis means determines the convergent state by setting as a precondition that a supply hydraulic pressure to the hydraulic control valve is more than a predetermined value.
 62. A diagnosis device for a vane-type variable valve timing controller according to claim 61, wherein: the abnormality diagnosis means determines whether or not the supply hydraulic pressure to the hydraulic control valve is more than the predetermined value, based upon information regarding at least one of an engine rotational speed and an oil temperature.
 63. A diagnosis device for a vane-type variable valve timing controller according to claim 54, wherein: a shaft for driving the first hydraulic control valve is integral with a shaft for driving the second hydraulic control valve.
 64. A diagnosis device for a vane-type variable valve timing controller in which each of a plurality of vane accommodating chambers formed in a housing of the vane-type variable valve timing controller is divided into an advance hydraulic chamber and a retard hydraulic chamber by a vane comprising: a first one-way valve disposed in a hydraulic supply passage of the advance hydraulic chamber in at least one of the vane accommodating chambers for preventing reverse flow of operating oil from the advance hydraulic chamber; a first drain control valve disposed in a first drain oil passage bypassing the first one-way valve and driven by hydraulic pressure; a second one-way valve disposed in a hydraulic supply passage of the retard hydraulic chamber in at least one of the vane accommodating chambers for preventing reverse flow of operating oil from the retard hydraulic chamber; a second drain control valve disposed in a second drain oil passage bypassing the second one-way valve and driven by the hydraulic pressure; a single first hydraulic control valve for controlling the hydraulic pressure supplied to the first and second drain control valves and the variable valve timing controller; wherein: during hold operating of holding a displacement angle of the variable valve timing controller (hereinafter, referred to as VTC displacement angle) to a target displacement angle, a control current of the hydraulic control valve is controlled to a predetermined holding current to close both the drain control valves in a side of the advance hydraulic chamber and a side of the retard hydraulic chamber to effectively function both the one-way valves in the side of the advance hydraulic chamber and the side of the retard hydraulic chamber; thereby preventing reverse flow of the operating oil from the advance hydraulic chamber and the retard hydraulic chamber and also controlling the hydraulic pressure supplied to the variable valve timing controller; during advance/retard operating of displacing the VTC displacement angle to the advance direction or the retard direction, the control current of the hydraulic control valve is controlled to open either one of the drain control valves in the side of the advance hydraulic chamber and the side of the retard hydraulic chamber in accordance with the displacement direction so that either one of the one-way valves does not operate; and further, the hydraulic pressure supplied to the variable valve timing controller is varied, thereby displacing the VTC displacement angle toward the target displacement angle, further comprising: abnormality diagnosis means adapted to determine whether or not there occurs an open abnormality state where at least one of the drain control valve and the one-way valve remains to be opened, based upon a changing amount of the VTC displacement angle within a predetermined period during the holding operating.
 65. A diagnosis device for a vane-type variable valve timing controller according to claim 64, wherein: the abnormality diagnosis means calculates a difference between a VTC displacement angle immediately after start of the holding operation and a VTC displacement angle at elapse of the predetermined period to determine presence/absence of the open abnormality state in at least one of the drain control valve and the one-way valve based upon this difference.
 66. A diagnosis device for a vane-type variable valve timing controller according to claim 64, wherein: the abnormality diagnosis means detects a maximum value and a minimum value of a VTC displacement angle from a point immediately after start of the holding operation until a point at elapse of the predetermined period to calculate a difference between the maximum value and the minimum value, determining presence/absence of the open abnormality state in at least one of the drain control valve and the one-way valve based upon this difference.
 67. A diagnosis device for a vane-type variable valve timing controller according to claim 64, wherein: the abnormality diagnosis means detects a maximum value and a minimum value of a VTC displacement angle from a point immediately after start of the holding operation until a point at elapse of the predetermined period to calculate a deviation between a target displacement angle during the holding operating and the maximum value and a deviation between the target displacement angle and the minimum value, determining presence/absence of the open abnormality state in at least one of the drain control valve and the one-way valve based upon these two deviations.
 68. A diagnosis device for a vane-type variable valve timing controller in which each of a plurality of vane accommodating chambers formed in a housing of the vane-type variable valve timing controller is divided into an advance hydraulic chamber and a retard hydraulic chamber by a vane comprising: a first one-way valve disposed in a hydraulic supply passage of the advance hydraulic chamber in at least one of the vane accommodating chambers for preventing reverse flow of operating oil from the advance hydraulic chamber; a first drain control valve disposed in a first drain oil passage bypassing the first one-way valve and driven by hydraulic pressure; a second one-way valve disposed in a hydraulic supply passage of the retard hydraulic chamber in at least one of the vane accommodating chambers for preventing reverse flow of operating oil from the retard hydraulic chamber; a second drain control valve disposed in a second drain oil passage bypassing the second one-way valve and driven by the hydraulic pressure; a single first hydraulic control valve for controlling the hydraulic pressure supplied to the first and second drain control valves and the variable valve timing controller; wherein: during hold operating of holding a displacement angle of the variable valve timing controller (hereinafter, referred to as VTC displacement angle) to a target displacement angle, both the drain switching valves in a side of the advance hydraulic chamber and a side of the retard hydraulic chamber are closed to effectively function both the one-way valves in the side of the advance hydraulic chamber and the side of the retard hydraulic chamber; thereby, the hydraulic switching valve is controlled to prevent reverse flow of the operating oil from both the hydraulic chambers and also a control current of the hydraulic control valve controlling the hydraulic pressure in the each hydraulic chamber is controlled to a predetermined holding current; during advance/retard operating of displacing the VTC displacement angle to the advance direction or the retard direction, either one of the drain switching valves in the side of the advance hydraulic chamber and the side of the retard hydraulic chamber is opened in accordance with the displacement direction to control the hydraulic switching valve so that either one of the one-way valves does not operate; and further, the control current of the hydraulic control valve is controlled to vary the hydraulic pressure in the each hydraulic chamber, displacing the VTC displacement angle toward the target displacement angle, further comprising: abnormality diagnosis means determines a convergent state to the target displacement angle of the VTC displacement angle at changing the target displacement angle to determine whether or not there occurs a closed abnormality state where the drain switching valve remains to be closed, based upon the convergent state.
 69. A diagnosis device for a vane-type variable valve timing controller according to claim 68, wherein: the abnormality diagnosis means measures, as data representing the convergent state, continuing time of a state where a deviation between the target displacement angle and the VTC displacement angle is more than a predetermined value to determine presence/absence of the closed abnormality state in the drain control valve based upon this continuing time.
 70. A diagnosis device for a vane-type variable valve timing controller according to claim 68, wherein: the abnormality diagnosis means measures, as data representing the convergent state, elapse time from a point where a deviation between the target displacement angle and the VTC displacement angle is more than a first predetermined value until a point where the deviation is less than a second predetermined value smaller than the first predetermined value to determine presence/absence of the closed abnormality state in the drain control valve based upon this elapse time.
 71. A diagnosis device for a vane-type variable valve timing controller according to claim 68, wherein: the abnormality diagnosis means determines the convergent state by setting as a precondition that a supply hydraulic pressure to the hydraulic control valve is more than a predetermined value.
 72. A diagnosis device for a vane-type variable valve timing controller according to claim 51, wherein: the abnormality diagnosis means determines whether or not the supply hydraulic pressure to the hydraulic control valve is more than the predetermined value, based upon information regarding at least one of an engine rotational speed and an oil temperature. 